Wild Electrical Issue Kicking Our Butts With Headlight and Instrument Dimmer Switch

Hunter Dog

Active Member
Hello Everyone,
I hope everyone is keeping safe and getting ready to hit the car shows soon as I am.
My local mechanic and I have been working for days on an electrical issue on our 86 GN project car.
Issue is this:
Pink and Purple wire show they are grounded but we feel from all we can research they should NOT be. Fuse is NOT being blown. Headlight switch and instrument panel dimmer switch are controlling things like the marker lights, tail lights, tach/boost on instrument cluster, the usual start up lights come on we toggle these switches and if we roll the dimmer switch up and down. We have pulled them and bypassed them and we will have the issue. Where in the world are we going wrong ? Please help as we are desperate. We have pulled ignition switch and pulled fuse box twice in looking for this. We have pulled wiper motor looking behind this area. We have been in the trunk. We have cleaned up all grounds we can find under the hood, inside the car and in the trunk. We have printed diagrams from onefootinthegrave site and anywhere else we can find info on the 86 GN. We have checked the option codes in the trunk and it does not show theft option which we eliminated.

We would sure appreciate another angle.
Thank you for your time. Once we get to the bottom of this we will repost for others to hopefully save a lot of time if this ever comes up.
When turning the key to the on position (not actually turning the key to start the car) one of the boost lights comes on in full and the other three normal lights go off. If you turn on the headlights and/or in the interior dimmer switch and roll it down, the other boost lights comes on, marker lights come on, tail lights come on. These two switches are controlling all of these things as if they are somehow touching another wire or wired up to control things they are not supposed to. Dimmer switch should only control the interior lights, not the boost, tail lights, marker lights. Headlight switch same thing. When we toggle it the lights on dash light up as if it is about ready to be turned over to start. We removed the switches to eliminate a bad switch as causing all the issues.
Suggestion. Get an idea of what the current draw is when you turn the key. Start pulling the fuses one buy one as you watch all the lights and the current draw. Even a lamp holder can be shorted without a bulb in it, causing a back feed through other devices and bulbs that are still part of a normal circuit. A good switch still creates a resistance when turned on, and a not so good switch can create a resistance that is not enough to blow a fuse, but great enough to cause troubles that you would like to shoot. Hence the name, troubleshooting.
A high school auto shop teacher presented the class with a car that was crank but no start. None of us could figure it out. He had stuffed a Juicy Fruit gum wrapper down the high tension tower of the ignition coil. The foil on the wrapper would allow enough voltage to cause a spark plug to look like it was firing, but not enough to allow the car to start.
I feel your pain. And thank you for your concern about our safety.
Sadly I don't think there is an easy answer. I'd be looking for bogus alarm install, hacked wiring due to ignorant installers and possibly mice chewed areas. Maybe someone tried to install theater style auto dimming courtesy lights.
I know you have checked all your grounds.
But it sounds like it still might be the problem.
Check the integrity of your fusible links down by the starter also.
Good luck, these type of problems will try the patience of a saint!
Thanks for the input so far from a few of you willing to spend a little time and offer some opinions. Car does NOT have twilight sentinal.
We are going to get back at it on Wednesday after a few days to review notes, gather input, do more research and step back and punt.
No doubt this is a real test in patience !
Thanks again...
I somewhat enjoy the challenge of an electrical problem until it quickly becomes a nightmare. Your problem is truly a nightmare. Hoping to help. Did this vehicle ever have an aftermarket alarm? I recently removed all remnants of an old Viper system from my GN and discovered the installer connected alarm wiring to both the factory headlight switch (to flash the parking lights) and the dash light dimmer switch for the courtesy light circuit. I’m betting you have already but make sure no stray aftermarket wiring isn’t dangling from those switches. Good luck.

We have the analog dash.
We got it working finally after maybe 15 man hours.
First thing we did is check all bulbs in tail lights and turn signals and marker lights and all were good.
Because there appeared to be multiple issues with the lights as described above on the dash /instrument cluster and the other lights being controlled by the dimmer switch on the instrument panel and headlight switch to the left of it, we did clean up the ground behind the engine block on the passenger side which was covered in grease and the tube to the transmission check was also touching this (bent slightly forward) which could have contributed, unsure but suspicious. We also replaced the headlight switch. Before we replaced it we took apart the old switch, cleaned it a little and it appeared to work. Then we came back the next day and it did not work. We put the new headlight switch in and it appeared to finish the job. We also pulled the entire instrument cluster/dash and replaced one bad socket hat was behind the high beam and one bad bulb in the lower area behind the dash. We swapped the electronic sheet /clear paper or whatever is is called that is behind this part with another one. The one we put in was in better shape. So, we cannot say for sure any ONE thing was the cause, but it appears to have been multiple issues creativing havoc with the entire system.