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Discussion Starter #1
Neither the fuel or temperature gauges seem to be working on my 1970 GT. With the lead pulled off the temp sender, and the key on, I read ~6.5 V at the lead which goes to the temp. sender, which seems consistent with what I've seen in other posts for the limited/regulated voltage. With the lead going to the fuel sender still attached, I'm reading about 5.7 V at the point where the lead attaches to the sender. With the lines going to the fuel sender and temp sender detached, on turning on the key, the gauges do not move (grounding the line to the fuel sender with the key on does not make the fuel gauge move). I looked behind the gauge, and the brown ground seems attached, and I measure continuity from the gauge bezel to ground; so I think the ground on the gauge is OK. It seems to me that if the gauges weren't getting power properly, I wouldn't see voltage at the lines going to the senders. But it also seems unlikely to me that both gauges would go out with the same symptoms; it's more likely that there's something common to both that's wrong. I'd appreciate hearing any suggestions about what might be going wrong, and/or more tests to do.
 

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Mid-West Opeler
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I was told that if you take of the wire at the sender and ground the wire you will get a "FULL" gauge reading. the wire has to be good and the gauge is good. If you do not get a full gauge reading, then you are down to a bad wire or gauge. Never had a bad temp problem but the same may be the same.
 
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Über Genius
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When my fuel gauge wasn't working I checked everything. The voltage, the ground on the fuel tank, the variable return from the sending unit, continuity, etc.

Finally I tapped on the gauge glass and it works now.
 

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Just Some Dude in Jersey
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Check the red connector at the fuze box area under the dash. Both of those functions pass through that one. It may be partially unplugged.
 

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Discussion Starter #5
I was told that if you take of the wire at the sender and ground the wire you will get a "FULL" gauge reading. the wire has to be good and the gauge is good. If you do not get a full gauge reading, then you are down to a bad wire or gauge. Never had a bad temp problem but the same may be the same.
I'd think they would work the same way. So to have them failing in the same way, I'd think there must be a problem common to both; it should be either power or ground at the gauge, but I'm not seeing that so far. I may have to drop the panel and have a better look.
 

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Discussion Starter #6
When my fuel guage wasn't working I checked everything. The voltage, the ground on the fuel tank, the variable return from the sending unit, continuity, etc.

Finally I tapped on the guage glass and it works now.
I tried tapping during one of the tests I ran, just in case it was the simple solution I'd really like; but no luck with that.
 

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When my fuel guage wasn't working I checked everything. The voltage, the ground on the fuel tank, the variable return from the sending unit, continuity, etc.

Finally I tapped on the guage glass and it works now.
I still have to tap on the glass on my temperature gauge but it works:lmao:
 

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So it goes.......



I have been flicking my glass on my gas guage since the clock stopped working in the summer of 1973! AND that damn clock quit the very day I rolled 12,000 miles! The gas guage functions well after a flick or two on the glass...has ever since......Go figure. I just thought it might be typical.
 

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Discussion Starter #9
Red Connector

Check the red connector at the fuze box area under the dash. Both of those functions pass through that one. It may be partially unplugged.
I checked the red connector this morning. It looked to be properly seated, but I wiggled it a bit to try and re-seat it. That didn't help. But thanks for the suggestion; it was something that went to the commonality.

BTW: I saw in the service manual I have (actually a '72, not '70) that they said to check that ..."the ground wire (brown in color) for gasoline and temperature gauges is properly connected to the windshield wiper motor and is secured." I'd removed the screen at the base of the windshield covering the wiper motor, but did not see that wire. When looking at the red connector, however, I did see a ground post behind the lever controlling the driver side dash vent, with a brown (among others) attached. Do you think that's what the manual meant when it was talking about attaching to the wiper motor? Seems like kind of a stretch, but I guess that stud could be on the backside of the wiper motor.

BTW2: I also have been unable to get the (aftermarket) radio to power on. I've checked the hot side of the only in-line fuse I see in the general area of the radio, and it has 12 V. Not sure if there's anything common about the radio, temp, and fuel gauges. Maybe that's just a red herring; I guess alternatively it could be a wild goose.
 

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The ground wire to the wiper motor was for Kadett only. HTH
John
 

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Discussion Starter #11
The ground wire to the wiper motor was for Kadett only. HTH
John
Interesting. The manual section I was reading was called "Chassis Electrical and Instrument Panel GT Series", and the pictures looked correct, but what they were saying didn't match reality. Thanks for the information.
 

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Mark1, my wiring diag. shows that there is a brown( common ground for both ) wire, that goes from the gauges to the speedo casing. There are several connections at the speedo, in the past I have had to put new spade connections on there due to corrosion or loose fitting. Sounds to me this is where to problem, since you have power every where else. :yup:
 

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Discussion Starter #13
Temp Gauge is Alive

I was fooling around with the gauge pair trying to get another measurement of the resistance to ground from the bezel (as a possible indicator of the gauge being grounded), with a 25 ohm resistor between the temp. sender line and ground, when all of a sudden the temp. gauge sprang to life (I used 25 ohms because in the " Testing a GT Temperature Sensor" thread, wrench 459 indicated that 50 ohms read 195, and I happened to have a 25 ohm handy). Now the temp. gauge continues to pin high, on key on, with the 25 ohm in place. I guess this was a variation on the tap it a few times fix. Fuel gauge still not working; but I'm less concerned about the fuel gauge working than the temp. gauge.
 

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Fuel gauge

If you ground out the wire to the fuel sending unit, that will tell ya if the gauge is bad ( should show full ) or if it is the sending unit in the tank, because you now know the ground to the gauge is ok since the temp. is working.
 

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Mark, When the factory manual is written there are mistakes or typo errors and the corrections are sent out to the dealers and the tech's get that information but book printers that use the original factory printing do not get these updates in time for printing. When you read something from a service manual and it does not sound correct always check with someone who may be able to add more info. HTH
Our Opels have difficult service manuals to work with, so good luck with your project.
John
 
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Just Some Dude in Jersey
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If your car is from here in the northeast and the fuel tank sender has never been replaced, then it's probably toast. I put a brand new out of the box one in, about 5 years ago and 6 months later it wouldn't go past halfway. I took it apart again(I had taken it apart when I first got it to see what a brand new one looked like) and the center shaft was already rusted enough to bind the float. I had to sandpaper the shaft. Modern gas ain't like the old stuff.

Did your sender ever work? How long have you had your car? What's it's history?
 

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Discussion Starter #17
If your car is from here in the northeast and the fuel tank sender has never been replaced, then it's probably toast. I put a brand new out of the box one in, about 5 years ago and 6 months later it wouldn't go past halfway. I took it apart again(I had taken it apart when I first got it to see what a brand new one looked like) and the center shaft was already rusted enough to bind the float. I had to sandpaper the shaft. Modern gas ain't like the old stuff.

Did your sender ever work? How long have you had your car? What's it's history?
I don't know much of the history. The most recent owner was from OK, so it's not the northeast, but it sure isn't balmy LA, either. I think he had it a few years; mostly took out the supercharger the PO previous to him had put in, but then got hurt so he couldn't complete the restoration. I think it probably sat for more than a year before I got it; maybe longer. I have no idea how recently it worked.

In looking at the area around the top of the sender, it looks pretty clean; but it's in a protected area so it could look clean on top and still old.

Now that the temp gauge has started working, I'll have to retest the fuel gauge by grounding the sender wire at the tank. Right now it looks to me as though there's an intermittent ground to the gauge (probably at the gauge), so I think I'll need to make sure I test the fuel gauge, when the temp gauge is actually working.
 

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Honestly don't know if this is a contribution or not, but it's food for thought. I've honestly not sat down and studied the factory wiring diagram nor wiggled my way on my back to look what's going on behind the dash. My car is relatively stock so there was never a need to do so; but I am mindful there are a lot of hacked cars out there with plenty of owner modifications. And of course, the fact that we are dealing with a 40year old auto.

Just a few observations and thoughts: my temp gauge went out one time and a quick check showed the spade terminal was intact, but the wires broken except one or two hanging on the terminal at the sending unit.

I've found it interesting that while running at night, when I engage the dimmer switch, I notice a drop in water temperature of about 5-10 degrees. Dim the lights completely or shut off the parking lights, temp gauge goes back to normal temps. Without looking at the diagram, I assume the dimmer switch circuit may be grounded with the temp gauge circuit, but again, take note of the word "Assume"!

The other thing is I too have the Opel Temp Gauge Tap Syndrome. Occurs at start up, give it a tap as the temp comes up and I'm usually good to go. I'm thinking a nice cottage industry for someone would be Opel Gauge Restoration. 40 years of gunk in the air getting on the internal components of our gauges have resulted in bulky gauges.

Being from the KISS School of Hard Knocks, I'd look real careful at your terminal ends at these components and previous owner hack jobs, pinched wires, etc. I'm also thinking of SciFi Guys photo of his GTX blower motor and how Mr Mouse took up residence. I had a mouse do some good damage on my New Beetle engine bay harness last winter. They do love that insulation!

Wishing you happy hunting with your issue!

Best Regards,
Mike
 

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Both Fuel and Temp. Gauges now seem to work.

After the temp. gauge started working, more or less consistently, I did retest the fuel gauge by grounding out the sender wire at the tank, when I could actually see the temp gauge was working. The fuel gauge goes full at that point, so both gauges are OK. So I think it probably just was bad ground to the gauge pair that was the problem; initially always open, then maybe going to intermittent as I started fooling with the gauges; intermittants are always a pain to track down. Now it's just a question of whether I want to drop the panel at this time and see if I can see a likely culprit to fix, or wait until the next time they both go out.

BTW: This all started when I went to drain out the gas which had been in the tank for an unknown time, and I got way more gas (2 gal. +) out of the tank than I would have suspected I should for an empty gauge reading. Once I get the tank completely empty, I'll need to add some good gas, and see if the sender is working or not.

Thanks for all the suggestions & advice.
 

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Mark1, when I got my car 10 yrs. ago it had 1/2 a tank of gas, drained the gas, put new in. the sending unit works fine except for 1/4 to 5/8 tank of gas, just kinda floats between the two, won't give a steady reading. The old gas probably put a ton of varnish on the unit. Once removed, you might be able to clean the internals, then test with a meter. I have a new one for a winter project, should have done it this summer when I had the rear deck out and panel below rear window to repair ( hit in the back one too many times) :banghead::banghead: :yup::yup:
 
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