I guess that would help. It's a 1987 4 door.

 

The lights have more then one ground point.

For the left side the ground point is in front of the rear drivers side wheel wheel.

You might be better off running your own ground wire. There is another ground point near the drivers license plate area.

 

Update. Ran a ground from the battery to the rear and measured the voltage difference between there and the ground on the lamp housing, .2v. Not significant. Also checked the lamp monitor module, looked ok. Tightened all the screws on the lamp housings, problem gone. Had to replace one burned out lamp.

 

Nice! Thanks for the update and solution.

 

It may be an electrical ground problem.