Here is the scenario.
2001 F250 7.3. I just bought it. Hooked it up to my trailer and I don't have right or left turn signals. Everything else works great. Everything works great on the trailer. Hooked it up to my other truck to verify everything working. Checked my power at the turn signals and have power. I unhooked each light and tested the plug. Everything looks great. Replaced taillights and still nothing works. Verified that the replacement taillights are working.
Trailer has a box where wiring pigtail comes into and goes out for all the lights. Took cover off of it and checked power for turn signals here and power is good. Here is where the problem kicks in. When I plug the taillights back in at the back of the trailer I lose power. Looks like completing the circuit kills the power. Must not have been enough draw using my multimeter to kill it when I was checking. So it takes my problem to the truck and for the life of me I can not figure it out.
Any help would be awesome.

Factory connections for the wiring. Wiring was taped into to add a connection in the box.

I don't think it is ground because running lights are strong.

 

If I am understanding your post correctly, when you hitch it to your trailer, you lose the turn signals on your truck. Did you undo the tape to see what was changed. I am guessing a bad splice, but need to do more detective work. The starting point is to make sure everything on the truck is the way it was supposed to be before someone perhaps got creative.

Steve

 

Thanks for getting back to me Steve. Actually after writing my post I went back out and tried with jumper wires going from the plug in the bed of the truck to the distribution box on the trailer and low and behold everything worked. I then did the same with the plug at the bumper and everything worked. Through examination of the wiring from the trailer plug to the distribution box showed evidence of wiring being pinched at some point. Striped back insulation and sure enough there was my bad spot. So I just need to wire a new plug on the trailer and things will be right as rain. Guess writing everything down helped me clear my head.

 

I never lost turn signals on the truck that was good. Didn't have turns on the trailer.

 

I had a hard time following your post, but glad you found the culprit!

Steve

 

Congrats on the fix. I was trying to figure out if all was ok with the trailer. It appeared to me that maybe you tried it with another truck.