I've been having some problems with the rear tail light on my 54 1/2 ton. It seems that the bulb socket is not grounded, and I can't tell how this is supposed to happen. The wiring diagram shows a ground at the tail lamp, but my tail lamp only has two wires coming off it, one for the stop light and one for the tail light. Shouldn't there be a third wire for the ground, or is the grounding supposed to happen through the lamp housing?
Also, the PO had spliced into the tail light wiring to add a license plate light, and what appears to be a wire for a trailer. The connections were all twisted together (no solder), and looked very ragged. I just cut it all out so I could start fresh.
So what I have now is two wires coming from the front of the truck (as it should), and I've verified 6V on one wire when the brake pedal is depressed, and 6V on the other wire when the park and headlights are turned on. So I think the wiring from the cab is good and intact.
So you'd think you just connect the two wires from the lamp to the two wires from the truck, right? Well, that doesn't work. I tested the bulb I have, and here is what happens:
1) 6V to bulb filament #1, ground to bulb housing = filament #1 lights up.
2) 6V to bulb filament #2, ground to bulb housing = filament #2 (brighter) lights up
3) 6V to bulb filament #1, ground to filament #2 (or vice versa) = filament #1 lights up.
So, based on my tests, the reason why my tail and stop lamp aren't working as they should is because the bulb housing is not grounded. If it were, then the two filaments would work properly. The way it was connected before, only filament #2 would light up. And it would only light up when the brake was pressed and the park/headlights were off!
So, I'd really like to know how the tail lamp is supposed to be grounded!! This should solve my problems! Thanks.
