Hello, just bought a 57 F100. Tail lights not working when I bought it, however, previous owner ran new wiring. I installed new bulbs, but still did not work, so I checked the wiring with a test light all the way from the headlight switch on the dash and I have juice. Test light also goes on when I touch the socket inside tail light housing, but when I put the bulb in, it will not light. Another weird thing is that I get the test light to go on when touching the tail light metal housing itself, so I'm assuming it is some kind of ground problem. Do I need to run a separate ground from the tail light housing to the frame? Any help would be appreciated as these electrical issues can be a mystery to me.

 

The light housing should be grounded to the box and the box grounded to the frame. A problem with either ground point will cause what you have.
Yes.
Running a ground from the light to the frame would be one way to remedy the problem.

 

Hello and welcome to FTE. I still get a kick out of it when someone posts: "My XXX doesn't work and I don't understand because the PO just rewired!" HMMMMM.....Sounds a little suspicious!

There's two possible porblems:

It's possible your previous owner bought the old OEM style light sockets where one wire is power in and the second wire goes to ground. Then he tried to wire them in like modern two filiment, base grounded type sockets. In other words, he's got power running to both wires and one should be ground. That also means your sockets are hot and there is no ground.

If I'm right, then you need to remove those sockets, buy modern two pin, socket base grounded sockets, install them making sure you have a good ground from the socket to the frame of the truck (remember if the brackets are painted that may impede grounding).

Then run your signal light/brake light to one wire and running lights to the other wire in back; or, signal light to one wire and parking light to the other wire in front.

Yo can buy those sockets just abotu any where - NAPA, AutoZone, etc etc.

But, also, if you are using a test light and it is clipped to ground, then if you don't have a good ground to the frame, the light wil llight when you touch the housing because the power flowing through the bulb grounds through the housing, but somewhere, it's not making it to the frame/ground.

What yo need to do is test for continuety between the light socket and the frame with a little multi meter (set it to "0 ohms" and touch the light socket with one lead and a known good ground with the other. If the needle doesn't swing, you don't have a good ground. As I mentioned above, painted brackets or gaskets can impede a ground. Yu can always run a redundand ground by attaching a wire to your light housing and running it under to bolt onto a clean spot on the frame.

I'm aslo assuming since your test light is working, that he has a grounding strap from the frame to the engine, then battery cable from engine starter mounting bolt to negative battery terminal. In other words the frame is grounded.

 

Thanks for the help everyone, I decided to run a ground from each tailight to the frame and has so far fixed the problem. Now for the front parking lights........

 

I am running a 1.5 ohm flamethrower coil with the ignitor module on my 54 truck with 239 ohv engine and 12 volt conversion with no ballast resistor. My question is how hot should the coil get after engine has warmed up. I was working under hood and happen to touch coil and it seemed pretty hot. I am going to get a laser temp gun but was wondering if anyone knew what was normal and what would be considered to hot. Thanks