This is my second Ford F150 and both of them have had wiring harness problems. I had the first one fixed at a shop for about $200. I would like to try to fix this one myself if possible. Both trucks have the factory installed wire harness.
My problem with this one is I have no brake or turn signal lights on one side. I have runnning lights, but no brake or turn signal lights.

 

Welcome to the boards.

The wiring is pretty simple, but we need a little more info:

4 pin or 7 pin connector?
Which side doesn't work?

 

...........

 

This is the seven pin connector at the hitch. Then I plug in a four pin adaptor into that. I am not sure what side it is, but one of the three sockets has no power at all.

 

Using a 4 pin connector means there are 4 wires out:

BROWN:Tail Lights (Hot with headlight switch ON)
YELLOW: Left Brake Light
GREEN: Right Brake Light
WHITE:Ground

Turn signals interupt the brake light circut. So if the right brake/turn does not work check the circut of GREEN to WHITE for 12V with the headlights on.

 

Gee, I'd feel better if I knew you weren't laying under your truck right now; there may be a little more to this.

Did the trailer lights ever work?
Are the bulbs good?
Where did you get the 4 to 7 pin adapter?
Does it work?
Any "spare" fuses and relays in a little bag in the glovebox?

Inquiring minds want to know!

 

Make sure you check the underhood fuses. There's actually a fuse (each) for the right and left brake/turn signal - in addition to fuses for the r/l parking lights.

Happened to mine the other week - thought for sure I had a trailer wiring problem. Just a fuse!

 

Fuse #19 (10A) - Right turn signal / Brake light.
Fuse #20 (10A) - Left turn signal / Brake light.

 

I'll chime in and agree that the first thing you need to do is isolate which vehicle is the problem. I work at a marina and trouble shoot a ton of these things. I even built a handy-dandy in-line tester with idicator lights that shows if all of the correct signals are coming out of the tow vehicle. The biggest problem I find is a bad ground. The second biggest is blown fuses in the tow vehicle. Blown trailer bulbs are a distant third. Good luck!

 

Thanks guys. I recently bought a '94 F150 5.0. Has a seven pin connector that through an adapter runs to a 4 pin trailer. One of the sides did not work. Checking this board led me to check the fuses first and I found 2 were blown. Changed them and now everything works. Probably saved me at least 5 hours of aggravation...because I would have probably been trying to test the connections in the back of the truck. You guys and this board ROCK!!!!!

Rod