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When head lights are on low beam and they are really dim - Opel GT 1970 Model- how can I fix it - Here is what I know

7K views 73 replies 11 participants last post by  Will I. Finish 
#1 ·
I have been reading up on head lights and how they are routed through relays and how there seems to be a number of variations, on wiring, variations either made by the the PO, a mechanic trying to make it work, or made by the manufacturer depending on the year of the GT. I have spent three four hour afternoons lying on my back looking up at this fuse box, testing connections - trying to figure it out, and would appreciate some help if this sounds like something you have been through. So these are the facts:
  • Head lights are too dim on the low setting - I would guess around 50 % too dim
  • I replaced headlight wiring harness was with a new wiring harness in 2000 - not a 70 model as it had a few more wires than the one I was replacing - the car has been in a garage and has only been driven 2700 mile since that time although I believe the dim head lights go way back, I think back 39 years or so - when I replaced the head light wiring harness I assumed it would be cured
  • I have cleaned the 4 main contacts on the fuse box so they now register the same as a direct read from the battery/ starter solenoid so plenty of power to that point 12.3
  • There is an anomaly in the relay wiring - Looking at the instruction for relay testing - D which is on the 7 prong relay is suppose to be "white/yellow striped wire # 87 this wire splits which carry 7-prong relay output power to 5 prong relay inputs labeled E " - My GT has no wire attached to that prong that connection is plugged into the fuse box, laying on your back looking up, closest to front of car second from the left/ passenger side front - don't think this is part of the issue but not sure - this prong with wire attached and lights on reads 4.15 volts on the multi-meter - to my knowledge the car came like this and again I don't think that is part of the issue
  • All of the other prongs read around 9.5 on both relays, while the battery and the 4 main fusebox connections were at 12.3 - keep in mind that I have been doing a lot of testing over the past three days do that is why the battery is low, as it is new - that is the ones that are supposed to have power
  • The gauge lights work only on the speedometer and the tach - the amp meter idiot lights come on when car is turned on but not the gauge lights on the three small gauges
  • High beam low beam switch is working, blinkers, everything else - the passenger blinker indicator does double blink but still works fine
  • So just a thought, with the lights on the 9.5 on the relays would that just be a function of the power drain from 12.3 to 9.5 or should it read 12.3 as well. Do I need to retest this with the car running however in the past lights were also dim with the car running
  • I guess one possibility is the relay needs to be replaced but it does past the test - seems odd that the voltage is lower on all of the relay contacts except the one that is around 4.15
Thanks for your comments, Carl
 
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#2 · (Edited)
Carl, I am in the same boat with the gauges. They worked 10 days ago, now none of them work. I will figure it out. I take that back, the speedometer still works.

Sometimes the headlights need to be upgraded. they just get worn out and need to be replaced. I have used LED lights for all the lights on my GT. My lights wer not as bad as yours, but they were losing brightness little by little.

Bob
 
#7 ·
Carl, I am in the same boat with the gauges. They worked 10 days ago, now none of them work. I will figure it out. I take that back, the speedometer still works.

Sometimes the headlights need to be upgraded. they just get worn out and need to be replaced. I have used LED lights for all the lights on my GT. My lights were not as bad as yours, but they were losing brightness little by little.

Bob
Thanks Bob, My head lights are new, that is the old fashion three prong bulbs from the old days. Regarding the gauge lights funny that two out of 5 are working for me. I have a feeling that is going to be something came loose last time I took out the instrument panel will let you know if I figure it out. While I was spending all that time staring at my fuse box I did finally get around to fixing one thing that I have a feeling a lot of people have an issue with. The steering column wiring plugs into the fuse box. With the plugs removed I was able to use needle nose pliers to pull the inter housing, that the plugs fit into out to where they belonged - then cut a couple slivers, litttle under a 1/4 inch of wood off the width of a paint stir stick, which was the perfect length, and JB welded the seams using the wood to add strength. Worked like a charm and I don't know why I did not do this years ago. Any the plugs now go in all the way and will actually stay plugged in. Pretty sure this is what brought back my high beam switch.
 
#6 ·
  • Thanks Commodaren, We can rule out the battery as mine is brand new as is the alternator - with all the testing the battery had run down a little over the past three days as I am not running the engine in the garage, not yet anyway!! I will put a charge on it right now.
 
#4 ·
Well, dim headlights was always the traditional way I discovered that my battery wasn't charging due to bad alternator.....or weak battery, but you're not running the engine. As a general rule, you should be reading full battery voltage wherever you check the Head/Park light voltage, except the instrument panel dimmer switch output, which of course will vary.

So, step one is: Do you have full voltage at the wires plugged into your headlights? If you have full voltage at the headlights but they are still dim, then the headlights are the problem. Another way is to run jumper wires directly from the battery to the device, in this case: The headlight bulbs. 12 volts should make both the hi and lo beam circuits in the bulbs light up equally

At my Post Office job, we were taught a basic testing principal on day one: Go to the end of the circuit and test for power, if it's not there(or in your case not enough power), then go half way back in the circuit and test again, keeping dividing and conquering until you find the power loss. Power in our PO machines would sometimes go through 30 daisy chained switches, circuit boards, etc., so cutting the problem in half saves you from randomly testing 30 switches and jumping all over the place without a plan. After I was taught that principal I actually used it to fix a problem on my Opel just days after being taught it......and it was a lighting system problem.

In general, on our cars the problem is almost always at the colored connectors at the fuse box or with the grounding of the various devices. You can have full voltage going to a device, but the ground is poor. Grounding is such a problem in our cars that when I built my GTX car with a new aftermarket fuse box I ran ground return wires back from every single light and device back to a single grounding point in that area. I have 3 of those points: One in the engine compartment on one of the big bolts on the brake booster support bar, one behind the dash, and one behind the seats under the luggage shelf. Nice stainless steel bolts on bare metal at each location. You must of course then also make sure that your negative of the battery has good ground to the body and engine, I use a stainless bolt screwed in at the normal engine/battery grounding point on the passenger side frame rail next to the engine.

Give that stuff a whirl and check your colored fuse box connectors(jiggle the ones that have lighting power while you are testing to see if it makes the power reading on your voltmeter fluctuate.
 
#13 ·
Thanks Gordon,

I spent another 4 hours reading, testing, experimenting - felt like science class all over again. Thanks for all of the information! Checked your recommendations:
  • I recently removed my engine to chassis strap and cleaned it really well and both connections - also checked the head light grounds near the master cylinder - all good
  • My ground to the battery is also stainless - my power reads the same at the battery, starter solenoid and the 4 main terminals in the fuse box - this morning 12.7
  • I checked the low and high beams using a negative ground from the battery which made no difference
  • Something that was surprising, while attaching an extra bulb that I have directly to the battery both + and - The brightness was pretty close to the bulbs installed in the car. That was straight 12 volt - voltage could have dropped a little from the testing but still I was expecting a big difference at least on the low beam setting
  • Speaking of science class, while I had the hats off the head lights checking the voltage I happened to touch that ground wire from the negative battery terminal to the white wire and I was expecting sparks to fly, like when I touch the yellow wire by mistake but guess what - the lights got a lot brighter and the voltage meter read .37 and no sparks - I don't know much about electricity but what am I missing here. Again I touch that extra negative ground to the white wire and the lights got brighter?
  • I then discovered that I had in fact attached the wrong wires to the wrong prongs so now they are correct with yellow to the left brown in the middle and white on the right - good news is that the voltage went from a little over 4 to 5.6 for the low beam and is now over 10 volts for the high beams. Making progress...
 
#5 ·
This will be an interesting read/ Diagnosis. I'm glad you brought this up Carl. When I bought my gt (73) Among all the things that didn't work including every aspect of the head lights not locking open or closed very hard to turn and just not working at all. My son and I pulled the buckets and all the parts that were attached. We found the bucket actuators rusted up and extremely dirty, the locks stuck all the micro relays shot and bypassed and the wiring from the light bulbs to the fire wall a disaster and all most nothing more than a rats nest of frayed wires. Once we corrected all there was from the fire wall to the lights we were shocked that the main relays in the fuse panel still worked. we can roll the lights to the locked position and reverse with two fingers. However low beam is as you say so dull yellow/orange when we drove at night we had to run on high beams to see anything. We just assumed that this is what it is and would replace the light bulbs later and see if it helps.
What I do find interesting is not only the extreme difference in the brightness from low to high but the clarity of the light as well. I'll keep tuned in to see what the outcome becomes. We weren't in any hurry to pursue the fix simply cause we/I don't drive it at night anyway But if I do or have to it would be nice to see where I'm going and not have oncoming traffic flashing me cause I'm running on high beams to see
 
#8 ·
A common wet type battery should never be drained to less than 50% of its capacity to avoid sulfation of its lead plates. The result will be a lower capacity for every discharge over 50%. And a battery should also always be stored fully charged between usages. I have an 80Ah gel battery for my electric 55lb Minn Kota fishing motor that is still going strong after 9 years of use, but I have never discharged it over 50% and always charged it full immediately after coming home from fishing .
 
#9 ·
Providing battery voltage is correct. 99% of the time dim lights, signal crossing, gauges moving when they shouldn't, etc. can be traced to poor grounding. Electricity will search for a path to ground and without a proper one, it will take any available route it can find to get there, usually affecting something else along the way. Opel's in particular have exceptionally poor grounding, a fact that only gets worse with age. Fortunately testing for a possible grounding problem is one of the easiest things to do. Clip a long wire to your negative battery post and touch the other end to the ground terminal of the headlight, gauge or whatever you are having a problem with. If it's a grounding issue your problem will disappear. Obviously it should go without saying, be sure you know EXACTLY which terminal is the ground point.
 
#10 ·
  • There is an anomaly in the relay wiring - Looking at the instruction for relay testing - D which is on the 7 prong relay is suppose to be "white/yellow striped wire # 87 this wire splits which carry 7-prong relay output power to 5 prong relay inputs labeled E " - My GT has no wire attached to that prong that connection is plugged into the fuse box, laying on your back looking up, closest to front of car second from the left/ passenger side front - don't think this is part of the issue but not sure - this prong with wire attached and lights on reads 4.15 volts on the multi-meter - to my knowledge the car came like this and again I don't think that is part of the issue
I am not sure what diagram you have, but I'm trying to interpret the above based on reading the FSM schematic.

That Wht/Yel wire between relays sounds like the heavy 12 ga wire that should feed the power from the 7 prong headlamp relay into the 5 prong headlamp dimmer relay. That 5 prong dimmer relay sends the 12v headlamp power to either the high or low beam filaments in the bulb. It sounds like someone moved that power feed to one of the 3 other outputs of the 7 prong headlamp relay, which are on the 3 positions on the fuse block that feed to the license plate lamps, tail and parking lamps, etc. Why this was moved, IDK, but it is possible that the main headlamp contacts got burned out in the 7 prong relay, and someone moved it to one of that relay's other contact outputs.

If it is really reading 4.1v on the prong feeding power into the 5 prong dimmer relay,, then that is a big problem; that voltage into the 5 prong relay should be only a few tenths of a volt lower than the battery voltage at worst.

Do as Gordo sez, and with the low beams on, measure the voltage at the4 headlamp itself on the low beam side. If it 4.1v, then your problem is in that wire feeding power into the 5 prong relay. Check the voltage where that Wht/Yel power feed wire connects into the fuse box. It that is also at 4.1v, then the problem is in the wiring between the fuse block point and the 7 prong relay...OR, that other contact in the 7 prong relay feeding that point on the fuseblock is just not designed to handle the headlamp current, or is also burned.

If the above guesses are right, then you are probably looking at a new headlamp relay. The fact that you have 9.5v out of the other 7 prong headlamp relay contacts going to the fuse block sez that something is very probably burned up in the headlamp relay. Then you can properly connect the power feed into the 5 prong dimmer relay to the main power output of the 7 prong relay... as it should be.

As a test of the 5 prong dimmer relay, you can disconnect that Wht/Yel power feed wire going to the 5 prong relay and temorarily jumper battery power directly into that wire; the headlamps then should be fully bright if there are not other wiring problems between that dimmer relay and the headlamps, and that relay's contacts are not also burned on either high or low beams contacts.

Hope that helps!
 
#14 ·
I am not sure what diagram you have, but I'm trying to interpret the above based on reading the FSM schematic.

That Wht/Yel wire between relays sounds like the heavy 12 ga wire that should feed the power from the 7 prong headlamp relay into the 5 prong headlamp dimmer relay. That 5 prong dimmer relay sends the 12v headlamp power to either the high or low beam filaments in the bulb. It sounds like someone moved that power feed to one of the 3 other outputs of the 7 prong headlamp relay, which are on the 3 positions on the fuse block that feed to the license plate lamps, tail and parking lamps, etc. Why this was moved, IDK, but it is possible that the main headlamp contacts got burned out in the 7 prong relay, and someone moved it to one of that relay's other contact outputs.

If it is really reading 4.1v on the prong feeding power into the 5 prong dimmer relay,, then that is a big problem; that voltage into the 5 prong relay should be only a few tenths of a volt lower than the battery voltage at worst.

Do as Gordo sez, and with the low beams on, measure the voltage at the4 headlamp itself on the low beam side. If it 4.1v, then your problem is in that wire feeding power into the 5 prong relay. Check the voltage where that Wht/Yel power feed wire connects into the fuse box. It that is also at 4.1v, then the problem is in the wiring between the fuse block point and the 7 prong relay...OR, that other contact in the 7 prong relay feeding that point on the fuseblock is just not designed to handle the headlamp current, or is also burned.

If the above guesses are right, then you are probably looking at a new headlamp relay. The fact that you have 9.5v out of the other 7 prong headlamp relay contacts going to the fuse block sez that something is very probably burned up in the headlamp relay. Then you can properly connect the power feed into the 5 prong dimmer relay to the main power output of the 7 prong relay... as it should be.

As a test of the 5 prong dimmer relay, you can disconnect that Wht/Yel power feed wire going to the 5 prong relay and temorarily jumper battery power directly into that wire; the headlamps then should be fully bright if there are not other wiring problems between that dimmer relay and the headlamps, and that relay's contacts are not also burned on either high or low beams contacts. I think the reason it was moved is because that vacant prong D is only carring around .16 voltage.

Hope that helps!
Thanks Bob,
  • Regarding your first paragraph - I think you are right as the prong on the end of the row of 4 is empty, however the instructions from OGTS call out that wire D from DIJK to be for White yellow striped wire (87) - this wire splits into two wires which carry 7 prong relay output power to 5 prong relay inputs labeled E. And by the way those two prongs are reading over 10 volts. That vacant prong is in fact carrying around .16 volts???
  • I did the test you mentioned adding 12 volts to the the white yellow power feed wire-which is currently at 5.65 volts and non difference to the low beam brightness - so I guess this is telling me about a new relay being in my future
 
#11 ·
First of all, it is imperative that the battery be fully charged. If it is not fully charged, strange and unexplainable things will happen. I can give examples.

You do not say but the suggestion is there that the high-beam function works satisfactorily -- the lamps are bright. This being the case, then you can eliminate "bad ground" as your problem. Each sealed beam is grounded individually (the right-side beam is co-grounded with the right-side indicator lamp switch). Otherwise, the two other grounds are at the high-beam switch on the steering column, which obviously works; and the #85 terminal on the headlamp relay.

With the high beams working, it would appear that the issue lies with the dimmer relay. The #12 Yellow wire connected to the #56B terminal is your low beam. Connect a known hot wire to this connection and see if the illumination improves. If it does, then either the connection at the dimmer relay is poor or the relay itself is gone. Otherwise, check the connections at the sealed beams. A defective headlamp relay or bad connections at any of the terminals would have an adverse effect on both high and low beam functions.
 
#12 ·
Manta raises a good point that I failed to address because of a bad assumption on my part, that the relays are all connected properly. However, the fact that the high beams do work would suggest that the connections are correct. But the current path of the circuit is as follows:

The 12-g Black wire from the hot side of the fuse block powers the headlamp relay microswitch behind the left-side headlamp unit. When the buckets open, this switch closes and connects a 12-g Yellow-Black wire

The Yellow-Black wire runs to post #85 on the headlamp relay, connecting internally an electromagnet that closes a switch connecting the 30/51 post with the #87 post. The 30/51 post receives current from a 12-G red wire from the hot side of the fuse block.

The #87 post has four connections. Three of them power the instrument panel lamps and the side marker/parking/tail lamps. Ignore them for the moment and concentrate on the fourth connection, the double-connected 12-g White-Yellow wire. One of these wires runs to the right-side headlamp indicator switch. Ignore it for the moment. The other White-Yellow connects to the #56 terminal of the Dimmer Relay.

Coming off the Dimmer Relay you have the 20-g Green wire connected to the "S" terminal, running to the dimmer switch. This apparently works as intended.

The Dimmer Relay is wired internally so that the dimmer switch grounds the 20-g Green wire, activating an electromagnetic switch that connects power from the #56 terminal to the #56A terminal

The #56A Post of the Dimmer Relay is the High-Beam function, with two 12-g White wires, one running to the high beam terminal of the sealed beams and the other to the high-beam indicator lamp on the instrument panel.

The #56B Post on the Dimmer Relay is the Low-Beam function with a 12-g Yellow wire to the low beam terminal of the sealed beams.

The headlamp open/closed indicator switches will not affect operation of the headlamps.
 
#16 ·
Thanks Michael,
  • Yes the high beam function works fine - it did not, the switch, last week but my fiddling around with the plugs from the steering column and getting a tighter fit seems to have corrected that problem.
  • 56B terminal has over 11 volts
  • Sealed beams are over 10 to 11 on high beam and 5.6 on low beam at the light bulb
  • The 87 four in line connections has one that is almost dead, maybe .16 volts so that wire is in the fuse box number 3 from the shifter and has a voltage reading of around 10.5 however at the prong connection it is 5.6
I am going to recheck all the numbers tomorrow with a fully charged battery, but based on the comments it appears that a new relay is required, or do I need both. When I added the 12 volts to the connection it still read 5.6.
Anyway I want to thank everyone for your suggestions/recommendations as it all served me well and I have learned a lot. Looks like after a retest tomorrow if nothing changes I will order the relay. I am pretty sure this is an issue that goes back to 1981. Its a long story but I have a specific memory about dim head lights in November of that year when my first daughter way born - like I said earlier I assumed that the new lighting wiring harness would have taken care of it but not so. This will be the first time I have purchase a new car one part at a time. It has no doubt been a challange but a lot of fun along the way. This forum keeps me going. Thanks all. Carl
 
#17 ·
If you have 11 volts at terminal #56B coming out of the dimmer relay and only 5.6 volts at the sealed beam, then there is a problem with the Yellow wire from Terminal 56B to the sealed beam. Possibly a bad connection or possibly a break. The wiring schematics do not show this wire going through any connectors -- it is a straight run from the relay to the beam. There is a connection up front branching the circuit to both headlamps -- this connection may be bad.
 
#18 ·
I am thinking that the terminal on the Headlamp Relay where you are measuring 5.6 volts may be terminal #86. This terminal is to be grounded. Internally, terminal #85 and #86 have between them an electromagnet. When the headlamps open ("On"), the micro-switch behind the left bucket mechanism closes as switch that connects power from the 12-g Black wire (from the hot side of the fuse box). to terminal #85 via a 12-g Yellow-Black wire that, because #86 is grounded, activates the electromagnet, causing a voltage drop at #86. You would have less energy too if you were run through a coil of wire.

This gets back to the earlier point that the connections to the various terminals have to be absolutely correct.

Red wire to terminal #30/51
Yellow-Black wire to terminal #85
#86 is grounded (color not indicated on schematics -- could be Brown or the relay could be internally grounded)
White-Yellow to one of the four connectors on Terminal #87

There are three other wires that connect to Terminal #87"
Gray-Green routes to the parking light switch, the instrument panel dimmer switch, and the license plate lamps (#1 fuse)
Gray-Red routes to the turn signal switch, the parking lamp switch and to the right-side side markers and tail lamp (#2 fuse)
Gray-Black routes also routes to the turn signal and parking lamp switches, and to the left-side side markers and tail lamps (fuse #3),
 
#22 ·
That is what is bugging me, Michael..... if you have the FSM, then there maybe a conflict or mistake in how it shows things. In all other relays in those diagrams that I have explored in detail, the FSM diagrams accurately show the innerds of the relays. If you follow that for the dimmer relay schematic, you can see that 56A has power to it at all times when the headlamp relay is on, regardless of whether it is high or low beam position. The external jumper on that relay from 56 to + is part of that circuit. This would be done for a low beam function only, obviously not for high beams.

But, at the same time, it shows another wire from 56A going to the high beam indicator in the dash; that does not makes sense to be connected to anything but the high beams, unless the high beam indicator works differently than one would assume.

So let me know if the internal conenctions in the dimmer relay shows up the same in your FSM diagrams; I am using the '71 FSM, figure 120-102 on page 120-84; it could be drawn incorrrectly.

Either way, I'd like to hear exactly what Carl is measuring at both 56a and 56b in both states. It is not 100% clear to me where he is finding that low voltage... at this relay or at the headlamp socket?
 
#23 ·
Just some past problems I had with my GT's switching from Low Beam to High Beam.
The column stalk has the switch on the turn signal stalk...pull/push
well that operates a latching relay, notice how you make the switch, you hear the relay latch,,click,click
so turns out ..bad ground again.. On the fusebox mounting stud, (threaded stud and nut holds fusebox)
the column mount point, 13mm bolt, theses are the grounds for the relays,

Dim Head lights... mum... bad grounds again..... On the driver side, inner fender (where the Radiator frame rail meets Inner fender fender... there should be two screws holding all the headlight grounds there,,
might have unburied in paint and corrosion...
Clean up the connection, new terminals and make sure the mounting location is not communized,, maybe start a new ground spot with self tapping screw

Check these three locations for """ A Good Clean Proper Ground ((-)) "" and surely your problems will be less..LOl
Engine Electrical wiring Wire Automotive engine part Nut
Motorcycle accessories Engine Carbon Electrical wiring Automotive engine part
Cable Wire Electrical wiring Gas Circle
Product Technology Cable Metal Leather
Brown Black Tan Snapshot Leather
 
#29 ·
Just some past problems I had with my GT's switching from Low Beam to High Beam.
The column stalk has the switch on the turn signal stalk...pull/push
well that operates a latching relay, notice how you make the switch, you hear the relay latch,,click,click
so turns out ..bad ground again.. On the fusebox mounting stud, (threaded stud and nut holds fusebox)
the column mount point, 13mm bolt, theses are the grounds for the relays,

Dim Head lights... mum... bad grounds again..... On the driver side, inner fender (where the Radiator frame rail meets Inner fender fender... there should be two screws holding all the headlight grounds there,,
might have unburied in paint and corrosion...
Clean up the connection, new terminals and make sure the mounting location is not communized,, maybe start a new ground spot with self tapping screw

Check these three locations for """ A Good Clean Proper Ground ((-)) "" and surely your problems will be less..LOl View attachment 431271 View attachment 431272 View attachment 431273 View attachment 431274 View attachment 431275
Thanks Mike, Pictures are always worth a 1000 words. I replaced the front wiring harness, over a freshly painted car, but it was not a 70 model wiring harness, perhaps a 71, and had more wires than I needed, that was 20 years ago so I have wires under there that I am not sure about now. So it looks like a close up in, what I think is your third picture, of the grounds at the fuse box screw. One of those wires should be from the 7 prong relay- can you show me where the other ground wire is coming from? Many thanks, Carl
 
#25 ·
So I did a search for 56-56a-56b relay and came up with a number of hits. This relay is/was also used in VW-Porsche-Audi as well as American cars in the late 1960s (and maybe others). In all cases, the low beam is driven off #56b and the high beam off #56a. Did a more refined search for internal circuitry and found a number of more simplified diagrams...that all show the same inconsistency that we see in the Opel FSM diagrams. Then I found this guy when I did a search for Meyle #100 941 0006. The diagram on the Meyle case clearly shows what is happening. Post #30 on the relay is comparable to the "+" terminal on our diagrams. Our cars receive power from the Headlamp Relay to terminal #56 via a White-Yellow wire that is also jumpered from #56 to "+" (#30 in the picture)
 

Attachments

#26 · (Edited)
Thanks Michael. The above relay is not so clear to me but this one is:

So yep, the low beams are on during the 'relay deactivated' state, with current flowing through 1 relay contact to 56b. The high beams are on during the 'relay activated' state, with current flowing through 2 relays contacts to 56a. (Assuming the external jumper is in place.) Making a lot more sense now, as single-headlamp-per-side systems ususally have the low beams off when the high beams are on. (Unlike old quad headlight setups, where the low beasm stay with the high beams.) So the internal wiring of the relay shown in the FSM schematic is not correct. Glad that is settled LOL

So if Carl has 11-12 volts in 56b in the low beam state, something is going on downstream in the wiring as Michael notes. The fact that Carl measured 5.6 v at one low beam terminal on the headlamp itself makes me want to think that possibly a ground is missing, or there is some other wiring snafu, and the 2 low beams are ending up connected in series. I keep trying to see if there is a sneak path with one of the headlight grounds disconnected, or a pair of wires to the bulbs terminal swapped, but have not figured out one yet.....
 
#27 ·
I am not sure I fully agree with you, as I believe the low beam filament remains on during both low beam and high beam operation. If you go back to the picture that I posted, and keep in mind there is a jumper that connects terminal #30 to #56 with the hot wire at #56 being fed from the Headlamp Relay, note the two parallel blades of the switch on the right. When the relay is in low beam mode as pictured, there is a direct connection from #56 to #56b through the left blade. When High Beam is activated, the two blades shift to the left, toward the electromagnet. This causes the left blade to shift from the #56b pole to the #56a pole, activating the High Beam, while the blade on the right shifts and reconnects the #56b pole to power from the #30 terminal, keeping the Low Beam illuminated.

We still do not know why the reading at the sealed beam terminal is half that of the same wire at #56b of the relay. I am not inclined to think it is a bad ground issue, as each sealed beam is grounded independently, plus the fact that the high beams work would seem to eliminate this possibility. Rather, I suspect the problem will be found where the Yellow wire from the dimmer relay to the left-side sealed beam meets and unites with a similar Yellow wire that runs to the right side beam.
 
#28 ·
And you may be spot on, Michael. I am just having trouble figuring out the diagram on the relay that you pictured. The diagram on the relay that I linked is different.

The connection of the 2 yellow wires at the first headlmap reached is certainly a prime suspect!

As far as what does what when, my recollection of all Asconas (which have a single headlamp per side like the GT) is that the low beam filaments go off when the high beams go on. And the '71 Kadett diagram shows that as well.

Also, I have to clarify what I said about quad headlamp setups. (This is going back in time LOL) One set of lamps is dual filament, and has low beam filaments as well as a high beam filaments. The other pair of lamps is has high beam filaments only. So when you go to high beam the first set has its high beam filament burning along with the high beam only set of lamps being on.
 
#30 ·
Umm, there has been an awful lot of words typed, but Mike Lane typed the ones that should have been read. He suggested you check the headlight circuit ground. This thread has become too long and convoluted to read. So read this (and apologies for the shouting):

CHECK THE GROUND CONNECTION WHERE THE BROWN WIRES ARE SCREWED TO THE BODY SHEET METAL BESIDE THE MASTER CYLINDER.

REALLY make sure that ground is good. Let us know if that is the problem.
 
#31 ·
Umm, there has been an awful lot of words typed, but Mike Lane typed the ones that should have been read. He suggested you check the headlight circuit ground. This thread has become too long and convoluted to read. So read this (and apologies for the shouting):

CHECK THE GROUND CONNECTION WHERE THE BROWN WIRES ARE SCREWED TO THE BODY SHEET METAL BESIDE THE MASTER CYLINDER.

REALLY make sure that ground is good. Let us know if that is the problem.
[/QUOTE]
Keith, In my last post I indicated that the wiring harness had been replaced on a freshly painted car, which I guess did not covey my meaning. However in my reply to Gordon, in an earlier part of this thread, I also said that I had "I recently removed my engine to chassis strap and cleaned it really well and both connections - also checked the head light grounds near the master cylinder - all good
So I think that question has already been answered.
I also mentioned that I used a long negative wire to check all connections to the head lights so pretty sure that the ground issues are covered with the exception of my last post when I inquired about one of two wires that I am not familiar with attached to the fuse box screw, one ground goes to the head light relay which I took off cleaned and reinstalled but the other I need clarification on, so I think progress is being made.
But you raise an interesting point, I have noticed, from time to time, that as the thread continues some people may make suggestions that have already been made earlier in the thread either because they missed the suggestion made earlier or they have not read the thread from the beginning and missed all that good information.
 
#39 ·
What is being described is EXACTLY what happens with a bad harness ground. It might be somewhere else, but that grounding screw beside the master cylinder is most often the culprit.

I have done away with the screw on mine and several friends GT's, instead installing an M5 bolt inserted from inside the wheel well, with a star washer on the head to ensure the bolt has a secure ground to the sheet metal. Then another star washer inside, then a nut to tighten the bolt tightly to the sheet metal. THEN I ensure that all the brown ground wires are properly terminated to eyes, which are then secured to the bolt with another star washer and nut.

Why do I go to so much trouble? Because that ground location holds 6 ground wires. And the screw from the factory is a POS.
 
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#34 ·
But that does not seem to be the problem here, does it? The OP stated that the high beams work, the low beams are dim. Did not say anything about the inability to switch back and forth. I will take your word for it as to what happens when the relays themselves are not properly grounded, but I do not understand this given the circuitry. If the headlamp relay is not properly grounded, it would seem that the headlamps would not work to begin with, as that relay would not work at all and no power would transmit between the #30/51 terminal and the #87 output terminals. The dimmer relay is grounded by the dimmer switch in the steering column, but the Usually On position of the relay internally has the #56 terminal connected to #56b, the low beam connector; if the dimmer switch or its ground is defective, it would seem that the high beams would simply not work.

You are correct in that, with high beam on, both filaments, high and low, are illuminated. I verified that this afternoon when I removed the headlamp cover and tested both terminals at the sealed beam with the high beams on: 10.3 volts at each, car idling.
 
#35 ·
If the wiring is in good shape, and or replaced, and this happens,, the problems in GT's is most likely a Bad ground,, first is the battery ground strap Fresh.. not green or covered in stink oil/grease and tarnish, that's the one on the battery negative copper strap to the battery box.. That and the one from the engine to the frame rail.. I also run another ground wire battery cable from the copper strap location and mount on the brake rail or the Alt. Mounting bolt to the engine.

Now the car is properly grounded... If you were to take a ohm reading from the fender location to the battery ground strap,, meter set for beeping contunty? and no beep... not anywhere near Zero,, that's resistence so anything attach there will not be 12.3 volts it would be less,,, hence the dim headlights.. but that's how my mind works,,,, I've really never had a relay go bad over all these years.. always the wire fault... Dead shorts from vintage old dried up wires, crossing each other with no insulation on them will weld the contacts in a relay closed.. if that was the case

The only other thing else
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Yellow Technology Cable Electrical wiring Wire
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is the harness is communized,,, see been there done that... Good Luck hope it all turns out right you Guys
Cheers
 
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