I bought my 1971 F-100 Sport Custom two weeks ago and am admittedly over my head. It's my first pickup and first project.

The back lights, rear turn signals, rear brake lights, and the side/running lights weren't working, but the headlights and front turn signals worked fine. So I replaced the fuses. Still nothing in the back. Then I replaced all the bulbs in back. Still nothing.

I figure it must be the wiring since it's just the back end lights that don't work. What is the next step? I'm trying to do all the labor myself to learn how to repair vehicles. Plus, I like working on stuff.

Thanks for the help!

 

When I first bought mine I felt like I was in over my head too. There were no internet forums then. Mine had wiring problems, coolant leaks, transmission leaks, bad brakes, no parking brake cables and a lot of other problems. The best tool you can have is a repair manual, but you made a good choice by joining this forum.
First place I would check for messed up wiring would be under the box. Someone may have hacked into it to hook up trailer lights. Also check to see if the rear lights are actually plugged in. You never know, someone could have unplugged them. Look for splices and peel back the tape to make sure that the right color wires are spliced together. In my case, someone had spliced the wrong wires together causing all sorts of goofy things to happen.
Another place to look for hacked wiring is under the dash, some people like to cut wires to install switches, custom interior lighting, etc.
I Hope this helps.

 

http://fordification.com/tech/wiring...-70_master.jpg This is your wiring diagram. You need a multi meter or, at the very least, a test light to troubleshoot.

 

Thanks for the suggestion! Someone had completely cut all the wiring for the back end. I tried to splice them all back together as best I could. Running lights, brakes lights and the passenger side back up light works. The driver side back up light still doesn't work and now NONE of the turn signals work; front, rear, AND instrument panel. But the emergency flashers work fine!

Did I just mix up the wires when I tried to splice them back together? If so, have I cause an even bigger problem?

 

Definitely go to the wiring diagram in Post#3 above. You will need it.
IIRC, the emergency flashers use a different fuse than the turn signals and brake lights. You may have blown a fuse by connecting these wires.

 

An electrician and instructor's suggestion: print out the wiring diagram, and then use colored pencils to locate and mark the circuit that you are working on. Just color one circuit at a time, and work on just that one, or else you will have a big ball of electrical spaghetti.

 

Remember, there are only FOUR wires going to the back of the truck:

running lights
back up lights
left turn
right turn


The left and right turn also function as the brake lights, and that is controlled by the turn signal switch. It either hooks them together for brake lights or separates them to blink for turn signal.

I don't know where you spliced the wires(inside the truck or outside)?

I know, there is nothing worse then fixing someone wiring nightmares. Especially if you don't know how it worked.

 

Got it all fixed!

Well, except for the driver side back up light and license plate light. Would that be a problem for the ground on each light?

I really appreciate all the help and input.

 

Yeah, it could be a bad ground. Also check for corrosion in the bulb sockets.
It's a good idea to use di-lectric grease in all exterior light sockets too.