license plate lights dilemma

[hcmor71]

I apparently have an aftermarket rear bumper on my 71 C10 that contains
2 license plate lights. My dilemma is that one side lights and the other side
will only light when the part containing the bulb is grounded against the hole
in the bumper, but when I put the bulb part into the part that plugs into the
bumper, light goes out. Am I missing an insulator or ground ? Thanks for your
thoughts.

[ncpetersc]

If the bulbs are wired in series grounding the first would make the second not light?

I wish I could sketch it out. Maybe I will try. But that's my thought.

Can you try grounding only one bulb, and see if both will stay lit? If you can, then the bulb not grounded need to be insulated from bumper(ground).

[ncpetersc]

This is only a guess, but if they are wired in series, they would actually both get 6v when on. But if you ground at point labelled 1 only bulb 1 would light with a full 12v.

[RustyPile]

If the bulbs were wired in series, any break in connection (hot or ground) or burned out filament would cause neither light to come on. Plus the series circuit would require the bulbs to be 6 volt, meaning applying 12 volts to a single bulb would immediately blow the bulb.. Unless someone has altered the wiring, the lights should be wired in parallel.. You have a bad ground connection when the troublesome light assembly is plugged into the hole in the bumper.. Clean the ground contact surfaces, removing any rust or paint, and your license plate lights should work as they should..

[FirstOwner69]

I'm not sure how your bulb socket is attached to the bumper. The bumper should provide the ground. A picture may help. Assuming it is directly attached to bracket which is attached to the bumper, is the socket tightly attached to the mounting surface? Try cleaning any visible paint or corrosion where the socket is attached to the bracket and where the bracket is attached to the bumper . Once clean, try winding some fine wire tightly around the base at the point of contact with the bumper. If your socket is as those I've seen, the contact in the base is spring loaded. Check to see if that is the case with yours by depressing the contacts for movment and that there is no corrosion in the base itself.

[hcmor71]

I finally resolved the license plate light issue by putting a separate wire
from ground in between the socket that holds the bulb and the bulb
cover that plugs into the bumper. I tried dielectric grease between the
two, but that didn't work. Very strange that I couldn't make contact
between the bulb socket and the bulb cap that plugged into the bumper.
Thanks.

[dmjlambert]

I had that same problem with mine, and added a separate wire to ground it as a temporary fix. The permanent fix was to replace the assembly. This is the style I have