Running new taillight harness?

[Somewittyusername]

Forgive me that if this has already been discussed, I am new here to the search function and didn't see anything that fit my criteria.

I recently bought a 1979 short bed Two-Wheel drive. There were no working tail lights so I have been working on building a harness. I have a few different diagrams, but, I am having a hard time figuring out where everything plugs in in the cab.

I tried to test for continuity on the old harness and didn't get any response so I basically copied it with a 3 wire trailer harness that I added a ground too. I have also built new LED tail lights to go in as well. So wiring for that is a little different but for the most part the same. Just need to know exactly how and where to tie it all in to make it function for both the brake light, reverse and turn signals.

Once again, if this particular subject has already been discussed, please forgive me.

 

[Matt69olds]

Dark green and yellow are you left and right turn signal AND brake lights. Their function is split up in the turn signal switch.

Brown is the taillights, light green is reverse lamps. And all of those individual bulbs needs a good ground.

Before investing a bunch of time in the project, verify the wiring to the rear of the truck is good. The smallest of the firewall connector (on the back of the fuse box under the hood) is the taillight connector. Use a test light and verify the turn signals, park lamps, etc work there before questioning your handiwork and the rear of the truck. If there is a trailer light connector, you can almost guarantee you need to start from scratch. You will probably find a dozen cheap crimp connectors and at least as many splices held together with cheap electrical tape.

 

[Turbo4whl]

There is a round plug like this next to the firewall under the brake master cylinder.

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Then another plug like it at the rear of the bed. There is no ground in that plug, the light assembly grounds to the body. Sometimes the rust between the body and the frame, the body looses it's ground. No rear lights will work if the body looses it's ground.

 

[Somewittyusername]

I'll have to go through and check all the grounds. I guess I hadn't considered that. The original wiring is still there and I was replacing it with a trailer harness as it has a lot of the same colors and is a little thicker wire. Weather here is crappy on and off in the midwest and I do all my work outside in the driveway. If its still nice today after I am out I'll report back tomorrow with my findings.

 

[Somewittyusername]

Well it was cold as heck last night but ended up figuring it out. Traced all grounds and swapped mechanical relay with led relay and had to bridge the two connections. Only got one side but it works! Sometimes the easier dumbest answers are the right one. Thanks guys!