Tail Light Wiring?

Oh man. That sounds like not a lot of fun there. I had to rewire one of my tail lights, a back up light, and a front blinker. Do you know if this is the orignial harness, of did someone put in a new harness sometime? This sounds like whoever put it in screwed up the wires really bad. Or maybe someone did a jury-rig on the brake pedal switch and its messing up the signal somehow. You might want to get a wireing diagram and start tracing wires as best you can. And maybe get one of those fancy circuit testers that lights up and beeps when you get it close to a wire with current in it. Has come in pretty handy for me when I couldn't get to an exposed part of the wire. Have a friend work the brakes and go around and try to find where the current cuts off. Good luck man. I hope you don't have to replace stuff. Wireing harness are expensive. Rewireing a car is something I unfortunatly have very little experience with. I looked under the dash and was afraid to mess with too much. So I ran new wires when I redid my AC, switches, fan, stereo, etc.

Scrasauge,
If you're lucky, it's just a faulty bulb and/or poor ground. Disconnect your battery! Replace ALL 4 -1157 bulbs (avoiding Sylvania, if possible) and while each bulb is out, clean, with a small brass brush, all contacts as well as the inside of the barrel of the socket, which provide the ground to the bulb. Lube the sockets with dielectric grease and remove, clean and replace the ground connections to the body. Over the years, I have had several 1157 bulbs develop tiny, hairline cracks in the base/insulator that allows a "slight" short from one circuit to the other, causing your exact symptoms. Please post back to let us know how you make out, as many folks here ask and get good advice to issues but never post back to confirm or debunk the advice. Oh yeah, like I said, "DISCONNECT YOUR BATTERY!"
HTH,
Gene

I had an issue like this, it turned out to be the crappy after market bulb sockets for the tail lights, make sure the bulbs are fitted properly and that both wires are making contact with the bulb.

I would go through and make sure the instrument cluster and taillight housings are properly grounded. At some point Ford added a ground wire to the cluster, if you have non add it. The taillights ground through the mounting studs.