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1966 Lemans Convertible. Rear courtesy lights in the armrests and the console light only dim when the doors are closed (or when the door switches are manually pushed in) but do not go out. Had to remove the bulbs to prevent battery drain. I’ve removed the door switches, cleaned, removed some paint in door jamb for good ground, even removed + wire in back of alternator to no avail. Grounding issue somewhere, any ideas? Thanks in advance.
 

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Yep --- although those door switches appear to be identical, they aren't. If they've been removed and reinstalled at some point in the car's past and weren't installed on their original "sides" (passenger side vs. driver side) it can cause the behavior you're describing. Power comes from the source and to the "first" switch in the circuit (I forget which side is first). That switch has two positions and has two wires connected to it. Power in, and power out. When that door is open, it connects power to ground and turns the light on. When that door is closed, it sends power through the "out" terminal to the other switch's "in" terminal so that when that door is open, it turns on the light. The way the circuit works is that the 'first' door either turns on the light or sends power to the other switch. The 'other' door switch is only 'live' if the first door is closed. If memory serves, you can also get this behavior if the wires on the 'first' switch are connected backwards. On my '69 they're both white wires which can lead you to think that they'll work connected to either switch terminal --- they won't.

Bear
 

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Great explanation Bear, thank you. I did unscrew the switches and pull them out about 4” or so, and both appeared to have only 1 white wire connected to them. I did not see 2 wires on either one. Maybe there are 2 wires going into 1 behind a kick panel? I’ll check for that next, thanks again.
 

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Great explanation Bear, thank you. I did unscrew the switches and pull them out about 4” or so, and both appeared to have only 1 white wire connected to them. I did not see 2 wires on either one. Maybe there are 2 wires going into 1 behind a kick panel? I’ll check for that next, thanks again.
66 only had a single wire to the door switch, when the door is opened the door switch shorts to ground and that white wire supplies the ground to the dome lights, the dome lights receive a constant un-switched +12 volts, the second source for a ground is thru the light switch, when you turn the light switch counter clockwise the lights will also illuminate. It is possible the light switch may be bad or a white wire somewhere under the dash is shorted to ground which will cause the lights to illuminate. Try unplugging the light switch and see if the lights turn off.

Go to this thread and look for the wiring diagrams for the 66;

https://www.gtoforum.com/f50/gto-wiring-diagram-scans-22042/
 

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Thanks Randy. I was able to confirm 1 single white wire to each door switch as you stated. Tried to follow them as best I could by looking under dash, both wires appear intact with no cuts, etc. I’d like to unplug the headlight switch as you suggest, is this possible without removing the dash? If not, I may wait until the winter.
 

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We just got a 71 LeMans 2dr Sport & after changing out a bad battery ground cable are now experiencing the issue with the dome light staying on. The light will dim with doors shut and we've messed with the white wires but still no luck. Hubs is trying to add an additional ground wire now to the motor. I'll update once "we" aka He figures it out lol.
 

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We just got a 71 LeMans 2dr Sport & after changing out a bad battery ground cable are now experiencing the issue with the dome light staying on. The light will dim with doors shut and we've messed with the white wires but still no luck. Hubs is trying to add an additional ground wire now to the motor. I'll update once "we" aka He figures it out lol.
We have seen this before. A power wire feeds only one side of the dome light. The other side is the ground wire. You may need a wiring diagram for your car to better follow the wire's path. They work in conjunction with the door jamb switch, and if like most of my older cars, the headlight switch when you turn it all the way I think to the left. The headlight switch uses a rheostat to make your dash lights bright or dim and the extreme left position will turn on the dome light for uses such as driving down the road and you need interior lighting. So there are a number of trouble spots that can be traced using a 12-Volt test light and Ohm meter if it comes down to it. There could be a wire that has rubbed through the casing and is grounding out as well. It just takes step-by-step wire tracing sometimes. Here is one of the many posts you can find using the Search feature above on the forum site - Interior lights wont turn off...
 

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Are your brake lights functioning corectly? I was thinking on mine when I had issues that some way the brake switch at the pedals involved. (Orange wire) worth a check.
 

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We just got a 71 LeMans 2dr Sport & after changing out a bad battery ground cable are now experiencing the issue with the dome light staying on. The light will dim with doors shut and we've messed with the white wires but still no luck. Hubs is trying to add an additional ground wire now to the motor. I'll update once "we" aka He figures it out lol.
It was a blown fuse!!! The courtesy lamp fuse was blown. Hubs just removed the blown fuse & everything is working correctly now with the good fuse in place
Are your brake lights functioning corectly? I was thinking on mine when I had issues that some way the brake switch at the pedals involved. (Orange wire) worth a check.
It was a blown fuse crazy as it sounds. Hubs changed it out with fresh one and it fixed the issue
 

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That’s Interesting Emily, Was courtesy fuse obviously blown or ‘hidden’ in the end cap blown? Sometimes Buss ones are blown but ‘appear’ visually ok looking at them and weird resistance things can happen..also wonder where the ‘dim’ voltage Was leaking from? Perhaps the Headlight switch rheostat?
 

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That’s Interesting, Was courtesy fuse obviously blown or ‘hidden’ blown? Sometimes Buss ones are blown but ‘appear’ visually ok looking at them and weird resistance things can happen..also wonder where the ‘dim’ voltage Was leaking from? Perhaps the Headlight switch rheostat?
Courtesy light but yeah fuse that little metal inside broke in half and a little black dust in the glass. Craziness thing but he just switched it out & lights went off once the courtesy fuse changed. Lights would go super bright with doors then shut & turn dim when the doors closed before we changed it out.
 
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