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Discussion Starter #1
I have a 1968 coupe with a strange problem. The driver's side rear brake light and turn signal are inoperative when I'm driving. The lights on the rear passenger side, and both front turn signals, function fine. However, if I turn on the headlights or parking lights, the driver's side tail light comes on, and the brake and turn signal on the driver's side starts working correctly! That is, the rear tail light gets brighter when I step on the brakes, and the turn signal works an flashes. Any ideas how to track this down? I have been staring at the wiring diagram but am not sure what to check. Everything else electrical on the car is functional, cigarette lighter, side marker lights, fog lights, headlights and hood mounted turn indicators all work. Thanks!
 

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Check your ground wire on that side, easiest to just turn the signal on and take a piece of wire and touch between the housing and a decent bare ground spot like the trunk latch area or something. See if the light starts working correctly. Also try replacing the bulb as the filament inside can short to the other circuit.
 

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Thanks for the advice. I tried the ground as you suggested, no change. I forgot to mention that the bulb was replaced with an LED sequential blinker, probably 10 or more years ago. I'll pull that tomorrow and see if there's an issue with the ground wire connecting to that board.
 

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I put a meter on the wires and everything checked out, ground wire and hot wires to the tail light, so I replaced the LED unit with an old two filament bulb and it worked perfectly. So, in the end it's the LED unit that was the problem, not the wiring. Thanks again.
 
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