[joedoh]

most aftermarket harnesses, even if they are wired for a GM column, come with two ways to wire for the turn signals to the rear, one system is a double bulb (separate brake and turn bulbs) and the other is a single bulb with double contacts (combined brake and turn bulbs). make sure you have the proper wiring at the column, sounds like that may be your issue in the rear.


yes, a double contact bulb will have two wires and the outside is the ground. it may sound too simple but make certain you have a ground wire from your battery to the cab, and another (heavier) one from the battery to the frame, and still another to the engine. these are called "differential grounds", not differential as in axle but differential as in ground potential. not having them introduces ground "loops", where power seeks a pathway to ground through any means possible. differential grounding gives a single point of ground potential, at the negative terminal.

for example, your brake lights are grounded, and that ground travels through the brake light filaments along the brake wire to the column and flasher and finally the switch, so when the brake/turn light is off, there is still a viable path to ground! when its on, though, that ground goes away. its a little remembered fact except to the old repair guys but 90% of the time a non working cruise control on an older GM was a bad bulb or bad ground at the rear of the car, because the cruise system grounded through the brake bulbs! (the cruise "shut off" when you stepped on the brake, this was an easy method!)

wiring isnt fun but it is rewarding from a "look what I did" factor. keep it neat! dont over do the zip ties, in fact years ago in avionics I learned how to aircraft lace wiring, always wanted to do that on a project instead of split loom.