Headlight relay bad?

[gtzero]

Hi Everyone,

My headlights don't turn on when I flip my lights. I recently had an accident where my passenger front was damaged. Everything worked prior to the accident. Now the bodywork is repaired and when I flip my lights...nothing.

There's also no warning light on the dash when the light buckets are not locked down. Hi beams don't work either.

There's juice from the fuse block to the relay, but nothing coming out of it. Does this sound like a relay problem or a micro-switch?

Thanks

[namba209]

Looking at JJ Wheatley's schematic, if your indicator light doesn't work, and there has been repair work involving the right headlight bucket, I would check the microswitch connection inside that bucket. There is only microswitch in that bucket and the wires are connected as follows: Gray/Green goes to common, Brown goes to normally open, and white/yellow goes to normally closed. HTH.

Ron

[mjewell]

here are a couple things to check while troubleshooting:

1) you say you have power to the relay...what about a ground?? without a relay ground, the relay won't work.
2) check these three wires which come out of the relay: gray/black, gray/red and gray/green. these are the wires to the lisence plate lights and the left and right side marker lights. do the side markers work? if they do, the relay is working. if they do not work, check the ground. if the ground is good, replace the relay.
3) the right side headlamp indicating switch (behind the right light bucket) does not actually do anything but turn the indicator light in the dash on & off. think of it as an "in transit" light that tells you when the lights are not locked down either open or closed.
4) from the left headlamp switch behind the left light bucket, there are two wires; red/black, which comes from the fuse block, and a brown/black which goes to the indicator light in the dash. the red/black should be hot, and the brown/black will be hot when the lights are closed.

do you have a schematic of the car? if not, get one. it is an invaluable tool when troubleshooting these types of problems.

let me know what you find.

mike

[gtzero]

Thanks Ron & Mike,

The marker lights work fine. All the lights work except for the headlights. So according to Mike, this would suggest that the relay is functioning.

The red/black wire should be hot when the headlights are "on"?
And the brown/black should be hot when the headlights are "off"?

Thanks again

[namba209]

Another area to check is the dimmer relay, it powers the headlights from the main relay, which does not power the headlights directly. There is a White/Yellow wire that goes from one relay to the other. The main relay has two wires attached at that point and one wire goes to the dimmer relay the other goes to the right bucket microswitch. HTH.

Ron

[gtzero]

I noticed those wire. My assumption is that current would flow from the fuse block to the main relay. And then thru these white/yellow wires to the dimmer and to the indicator switch.

Since these white/yellow wires are not hot, I assumed there was a problem in the main relay.

[namba209]

That could possibly be a bad relay, the schematic shows a buss bar going to all four contacts for the headlights, left and right running lights and the license plate lights, but they could be individual relay contacts inside the can. I don't know. It is possible to open the can and physically check the contact point surfaces to see if they are severely corroded or pitted.

Ron

[gtzero]

Thanks Ron,

I'll check it tomorrow. I'm beat. And it's dinner time. Thanks again for your help.

[nobody]

One thing I have to ask. What year is your GT? There were changes to this curcuit depending on your production date. I have seen 2 72's that were different, 69 is also done differently. Before you dig in too much make sure you are on the right page. I looked for the year of your car but didn't find one in your profile. I don't want to say something to get you off track.

[DESTEC]

IF you have a volt meter (or use a probe with a 12v light in it)
Check for 12v on the #87 contact of the head light relay ON THE terminal that has the 12 Wh/Y wire--it feeds the DIMMER relay.

The dimmer relay in an alternate-action relay that ports 12v to either the HI or LO beams (White or Yellow wires) IF your running lights come on (the gray/red, gray/green and gray/black wires) bet the fourth contact (yel/white wire is working too, but not necessarily). Even if the Dimmer Relay craps out; it will always have at least one OUTPUT hot, you will always have either a HI beam or a LO beam output. IF you have 12v going into it from terminal 87 of the HL relay

The running lights come on if you turn on the Parking Light Switch, too. Don't use that switch in this test.


Any help

JJ

[gtzero]

Hi Everyone,

I now have a replacement for my defective headlight relay switch. The only problem is I'm supposed to put the new relay inside the "can" that the old relay was in. The "can" being the metal jacket that the relay sits in and attaches to the side of the fuse block.

The new relay is basically a cube in shape. But my old relay and "can" is a cube but with the vertical edges of the cube rounded..."square peg in a round hole".

Firstly, how do I extract the old relay from the "can"?
And secondly, how do I secure the new relay inside the "can"?

Thanks

[pvcar]

well it sounds like u dont even need to put the new relay in the can u could just mount it on hte fuse block, but i do believ u jus pry around the bottom edge of the can to remove the insides, could u post pics may help.

[gtzero]

pvcar,

The new relay has no attachment point. That's why I asked how to secure it to the "can" once I get the old relay out. At this point, I'm thinking glue/cement. But if I ever need to do this again...

Sorry, no digital camera at this time.

[gtzero]

Hi All,

I thought I had it. I replaced the headlight relay and I had signal at all the grey/color wires but still no signal on the yellow/black wire from the micro-switch. So I took apart the passenger side head light bucket and checked the switch. I only checked the passenger side because that's where the body damage was repaired.

Before I did this, I didn't get the dash light for the headlights either. Now, after messing with the micro-switch, the headlights came on a couple of times. And then went off. I replaced the micro-switch and again no headlights. But I have the dash indicator light.

Now there's no signal at any of the wires on the headlight relay when the key is on. Did I somehow fry the relay?

I'm at the point of by-passing the microswitches and just wiring a toggle switch from the second fuse to the yellow/black terminal on the headlight relay. But if the relay is bad, then this won't work.

I'm confused now. Do you think the relay is dead?

thanks

[ConreroGT]

start back at the beginning. Find out where you have juice first. Get the 'ol wiring diagram out and start from the fusebox. If you have a short somewhere...the headlights have a bit of juice on them...they will melt and most likley cause a fire. Dont try to bypass anything yet.

Start with the basics of where you have power and go from there.

Be careful when messing with the headlight curcuit. If it goes....you'll have a bad day. Their a bitch to rewire.

Unhook the battery when appropriate.... Especially if you do continuity checks.


And take your time. The headlight curcuit isn't too difficult. It can only be so many things.

[nobody]

Your headlamp relay switch is on the drivers side. There should be 2 switches there, one is relay with yellow/ black and black wires, indicator switch with red/ black and brown/ black. Some 71 and 72 models the brown/ black is brown and a different size. Power flows from the second from right place on the fuse panel on the black wire to the relay switch. From the relay switch to terminal 85 on the headlamp relay on the yellow/black wire. There is a red wire screwed to the center of the fuse panel that supplies terminal 30/51 on the headlamp relay with power. Also check your ground from terminal 86 on the headlamp relay, no ground no relay action. to test your relay jump from the center posts on the fuse panel to terminal 85 on the headlamp relay, relay should close and everything come on. You can test this without removing the lights. Roll them open and put your jumper on. If you have lights then it is the black or yellow/black wires or switch. If no lights then it is relay or red wire supplying the relay. If memory serves me correctly stock wiring has the headlamps independent of the key switch. I know I altered mine to only work with the key on. Good luck and hope that helped


note; 69 and some 70's only have drivers side switches