Originally Posted by grtharris
Hikerdogs, Yes looks like there are 2 connectors and 4 splices before the wire gets to the ground (G-108). Do you have access to the Ford drawings it would nice to look at that ground stud?
yes I have access to the Ford drawings. I learned a long time ago to buy the service manuals when you buy the vehicle. In days of old some of the manuals took up 3 feet of shelf space and cost an arm and a leg. Fortunately they're now on DVD so I can print the pages I need and take them to the job.
Now for the good/bad news. The good news is that everything now functions properly. To make sure it actually was a ground problem I isolated the ground terminal on one of the trailer turn relays and put a jumper to a known good ground. I went back to the trailer hitch socket and everything worked as it's supposed to. I then started following the ground circuit back from the chassis terminal to the firewall. everything was intact, but still no lights when my jumper was removed.
I went inside the cab and started tracing the wires to the next connector. It was buried in a mass of other harnesses above the steering column so I decided to go to the relay panel itself and start tracing from that end. I couldn't get my hands behind the fuse/relay block so I removed it from the mount. I placed a probe from my multimeter to a ground wire at the back of the panel and the other lead to a known good ground. Low and behold it showed continuity. I turned on the ignition, flipped the directional light lever and went back to the trailer socket. Much to my surprise it worked. I then tried the other directional, the flashers, and the brakes. All are functioning properly.
I don't know what happened. Whether I had a poor connection at the relays, a poor splice in the harness, or a partially severed wire. Now that everything works it's going to be almost impossible to know what was wrong unless it fails again.