63 c10 tag light wiring issue.
 

I planned on helping my dad with a simple tag light install and have become a bit confused about the previous owners wiring.

I have the tag light mounted and grounded with just 1 power wire to hook it up. The simple thing in my mind is to splice it into the running light power wire. Once i found this wire, it was 2 yellow wires spliced with a black ground wire running to the frame.

Hooking my tag light power wire to it, everything thing gets dim but still works. If i take the black ground wire off of the 4 wire set nothing works.

Can someone please help me out and tell me why this ground wire is connected and essential to making the running lights work?

Re: 63 c10 tag light wiring issue.
 

Each of your lights should have it's own ground and the power wires to the running lights are brown. They may have faded to yellow over the years or the PO may have changed them. They can't be spliced to ground or you would be blowing the fuse.

Here is the wiring for the stock truck tail lights.

Attachment 1549328


The Yellow wire is left turn/brake light
The dark green wire is right turn/brake light
The brown is tail lights
The light green is back up lights
And the brown wire is for the license plate light.

You should be able to connect it to the either brown wire
and ground the plate light socket and the light will work when the headlight switch is pulled.

Look behind the distributor on the firewall and you should see the connector for the rear lights with the colors I described. Midway back inside the left frame rail should be another connector and farther back should be another one for the rear lights. Most of the time a previous owner will splice in a trailer harness and usually screw up the harness with some off color wires. Or they will ground out one of the hot wires and blow fuses then the lights won't work at all.

You can go to most Walmart stores and get the trailer harness and it will have the correct wires for the tail lights. It won't have the reverse lights though.