Hello everyone, I'm still working on my F100 wiring, here's the latest. The previous owner installed a GM column, and GM wiring harness in the truck. I've got the new headlight switch hooked up, got all the front lights working as they should, but can't get my tail lights working properly. I've re-wired the brown wire from the switch, to the back of the truck, yet the lights still don't work properly.

The problem is, with the brown, green and yellow wires hooked to the tail lights, they don't come on when the front ones do, but oddly enough, if I move the directional lever (while the truck is off) one light will come on, or if the directional lever is moved to the right turn position, both lights come on. I pulled a directional harness out of another column I have and hooked it up with the same results when I slide the directional contacts. I unhooked the green and yellow wires from the tail lights, thinking if just the brown is hooked up I should have driving lights, but only one comes on, even though they are sharing the same brown wire. Then to complicate things more, when the directional harness is connected and the directional is in the off position, lights off, the dash lights come on. I've followed all the wires from the tail lights, and don't see any bad connections, or erroneous grounding. (yes, the tail lights are properly grounded during all of this testing) I'm still trouble shooting, but thought I'd see if anyone had any ideas I may not have thought of. I may have made an error in the switch wiring, but can't understand why the fronts would work fine, and not the rears, especially since they both share the same brown wire on the switch for power. I know, this is confusing, I'll probably end up re-checking the switch wiring this weekend, then start following wires again.

 

I was having similar problems when I wired my truck. I gave up and went to the library and got the wiring schematics from the Mitchell auto manuals. I looked at the harness fuse box and matched the diagrams in the book. It turns out 87 Chevy truck harnesses are based on the 85-87 blazer harness. Anyways, It turns out the wiring was all right, the problem was I was not taking into account the amount of rear lights I was wanting to use the harness with.

That’s as much advise as I can give you, it will save you a lot of headaches. It is difficult to figure out what the previous owner did or had in mind. It sounds like the wiring in the fuse box may be crossed, but figuring the box out is a mess.

Rey

 

Thanks Rey, I didn't think of the fuse box. I've got the wiring diagram already, the column and harness is out of a 78 Monte Carlo, so I'll take a look at the diagram and the fuse box this weekend. Ken

 

Not sure if this will help, Not sure if this is what chop top was saying ??
But is it poss that the column and harness were used where the rear turn sig. lights were seprate from the brake lights.
Just a thought
Mike

 

The brown wire to the rear is always the running lights. They have no interaction between the turn signals or brake lights unless there is a grounding problem. Leave the green and yellow wires disconnected until you can get both tailights to work. If they don't work you have grounding problems with the sockets or bad sockets that are not making good contack with the bulbs. Take a test light and probe the running light contacts in the socket. Make sure the test light is grounded to the body. They both should be hot when the headlight switch is in the park light or headlight position. If you are OK there next connect the test light ground to the ground terminal in the tailight sockets and again probe the running light contact. I think you will find you have rusty or corroded sockets that are not letting the bulb body get a good ground. Good luck!!

 

Thanks everyone. I finally got them working. It turned out to be a combination of things. Poor ground in the sockets, a crossed 'brown' wire going from the front to the rear, and eventually, which may have been caused by all my experimenting, a blown fuse. Appreciate all the help, all the lights work great now.