I have a crew cab 1996 ford f-350 7.3, rebuilt with about 30,000 miles on motor and less than 10,000 on trans. I just did a body swap with another crew cab diesel, and when I turn my headlights on, my drivers side turn signal quits blinking and my torque converter unlocks and will not lock back up. I sanded all grounds to bare metal before putting back on, also cleaned up connectors. Any idea which one I may have missed? Seems like the only explanation. Or any possible other ideas? Probably a question for one of the experts!?

 

What about with the headlight switch in the parking light position? If that does it, check the rear bulbs. That's where the brake/turn circuit meets the park/tail circuit. A short between those two filaments in one of the rear bulbs, or between the two terminals in the socket, will energize the brake light circuit when you turn on the parking lights. That will in turn unlock the TC.

 

In the parking light position it also does it. I changed both rear bulbs and I changed the socket on the drivers side. Possibly a short in the wiring harness near the connector to the break light harness?

 

Could mixing one of the two grounds that come from the socket with the other be causing this issue? Maybe I made a mistake and put one ground to the opposite and that is causing my issue?

 

A ground is a ground.

Did you happen to install LED bulbs at the same time?

 

+1 on the grounds; they're all common.

Try removing both rear bulbs, see what happens then. If you still get the issue, you're on to something that it's probably in the rear wiring harness. There's a disconnect for that section up under the bumper, driver's side.

Oh, one other thing comes to mind - is there any trailer light wiring in the picture?

 

There are trailer lights. They are all tied in just before the connector to the harness that actually splits to both tail lights. So its is spliced into the section that runs along the frame rail up to the drivers side wheel well where it connects. This trailer wiring was done prior to my owning the truck and I am wondering if I have a bad connection in the cluster?

 

And as for the LED's no, there were actually LED's in it and I think one of the bulbs went bad so I just placed with two traditional bulbs.

 

Sounds like you have one of those tee connectors for the trailer light wiring at the rear harness connection. Yeah, disconnect there and retest.

 

Will do. I will just disconnect all of the trailer wiring all together and wire the plug back in how it was from factory, test, and see where I am at. Thanks!