My 86 GT has had issues with the none of the gauges working accept for the speedometer. I was assuming this was a bad ground as they all seem to be a sensor input. However when I would use the backlighting for the dash the door chime would ring, so I unplugged that and didn't have any issues until as of late. The headlights do not come down anymore and my running lights no longer come on when the headlights are on. Highs lows work fine as well as the brake lights. The "Pontiac" lights up as well.
the previous owner had the cooling fan switched in, to a relay, but what it is grounded by a green/black wire under the instrument cluster. I was also told the headlights were upgraded to the Gen II headlights, but I don't know the difference by just glancing at them.
Any schemtics or help on this matter is greatly appreciated.
I also swapped out the light switch from my parts car, an 85GT, and it didn't help or hurt the issue except the driver light now struggled to raise on its own power. Seems like bad great, runs alot longer than it should when I turn the lights off.
Phonedawgs you're the man, unless bloozeberry chimes in first. 😉

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[This message has been edited by tshark (edited 09-08-2018).]

Sounds like bad grounds perhaps. I dont know where they all are to help you much though.

The only thing that all of the gauges (except the speedo) have in common is the power source: the Gages Fuse. Check to make sure it's not blown and even if it doesn't appear so, try swapping it out for a known good fuse.

The headlight closing power and your running lights all get power from the Tail Fuse, so I would look for a blown fuse there to fix those problems.

If that doesn't start to cure at least some of the problems, then post back here and I or someone else can help troubleshoot further.

I will double check the fuses tomorrow. Then headlights were intermittent in the beginning, some days stay ing up after I turn the switch off but when I leave for work the next day they are down again. Seems now they won't retract. I guess should mention that the cooling fan runs all the time now, like the switch is burned and just a constant closed circuit, no matter the position.