Electrical Gremlin (Page 1/1)
Toddster JUL 12, 12:27 PM
OK, this one is bizarre. My third brake light works fine. But the rear brake lights are barely on...until I turn on the AC, then they light up brightly. There must be a short somewhere but I am damned if I can figure our where the AC and brake lights have a common path. Ideas?
skywurz JUL 12, 12:54 PM

quote
Originally posted by Toddster:

OK, this one is bizarre. My third brake light works fine. But the rear brake lights are barely on...until I turn on the AC, then they light up brightly. There must be a short somewhere but I am damned if I can figure our where the AC and brake lights have a common path. Ideas?



I would argue there is a grounding issue somewhere.
theogre JUL 12, 01:12 PM
Yup...
First step is Pull the sockets from taillights to look at actual bulbs.
Only 1 filament should be on just for brake lights. If both then you have ground problems.

Otherwise could be iffy ground anywhere.
Start cleaning/fixing all "grounds" in the engine bay.
See my Cave, Wire Service
Coat ends bolted/screwed to frame or block w/ silicon or brake grease.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Toddster JUL 12, 01:40 PM

quote
Originally posted by theogre:

Yup...
First step is Pull the sockets from taillights to look at actual bulbs.
Only 1 filament should be on just for brake lights. If both then you have ground problems.

Otherwise could be iffy ground anywhere.
Start cleaning/fixing all "grounds" in the engine bay.
See my Cave, Wire Service
Coat ends bolted/screwed to frame or block w/ silicon or brake grease.




Only the brake filament comes on when the brake is applied, not both. I have been through the schematics front to back and still see no connection to the AC and the brakes. It has to be a damaged wire somewhere. Ugh, I hate hunting wiring issues.
IMSA GT JUL 12, 10:28 PM
The only thing I can see in common with the tail light grounds is the trunk blower which I believe turns on with the AC. I don't know if that is somehow completing the circuit when you apply the brakes with the AC on?
Dennis LaGrua JUL 13, 05:32 AM
If you have a GT fast back there are three separate circuits that run the rear lights, tail light, brake/stop and turn. On the notchbacks there are only two that use a shared brake/stop and tail light circuit. All those circuits use a common ground which is a wire on a lug screwed to the frame under the wheelhouse liner. This sounds like you have a ground problem.

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Toddster JUL 13, 09:42 AM
I'll disconnect the light harness and test if from the junction box. At least that will isolate the problem fore or aft of that point. Then it is just a matter of chasing it down.