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I just bought a 91 and the weirdest thing is happening. a good 80% of the time in the middle of the day, when i park my car the headlight will turn themselves on and i have to cycle the light switch for them to turn off? Has any one else had this issue? ive tried pulling and cleaning fuses/relays. ive even disconnected the battery the clear the ecm. any ideas of what i could try next?
 

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I just bought a 91 and the weirdest thing is happening. a good 80% of the time in the middle of the day, when i park my car the headlight will turn themselves on and i have to cycle the light switch for them to turn off? Has any one else had this issue? ive tried pulling and cleaning fuses/relays. ive even disconnected the battery the clear the ecm. any ideas of what i could try next?
Wow, you do have a good one there Jakbaer. Your headlight relay has a "ghost" ground from an intermittent short to ground on the coil circuit( 85 to 86). Headlights are unswitched, meaning that the B+ supply to pin 30 of the headlight relay does not go through the ignition switch, but directly from the battery, so you can turn headlights on when no key is in ig switch. Sounds like the path to ground(normally the headlight switch) is 80% of the time finding another path to ground once key is shut off. Does it happen immediately at shutoff, or at some time later? My guess is the headlight switch itself is the culprit since cycling through the ground(on)/open(off) cycle shuts the lights off consistently when they come on with out being requested. And is it always just the low beams, or will highs or both low/highs that come on? I'll dig into the wiring diagram a bit, and get back to you.
 

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Discussion Starter #3
Wow, you do have a good one there Jakbaer. Your headlight relay has a "ghost" ground from an intermittent short to ground on the coil circuit( 85 to 86). Headlights are unswitched, meaning that the B+ supply to pin 30 of the headlight relay does not go through the ignition switch, but directly from the battery, so you can turn headlights on when no key is in ig switch. Sounds like the path to ground(normally the headlight switch) is 80% of the time finding another path to ground once key is shut off. Does it happen immediately at shutoff, or at some time later? My guess is the headlight switch itself is the culprit since cycling through the ground(on)/open(off) cycle shuts the lights off consistently when they come on with out being requested. And is it always just the low beams, or will highs or both low/highs that come on? I'll dig into the wiring diagram a bit, and get back to you.
It happens immediately at shut off. And it is only the low beams
 
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