I looked at all the light connections and “re-did the grounds”. After that the tail light worked but the blinker did not. Exactly the opposite of the earlier dilemma. Go figure. I then cleaned out the channel on the top left side side of the trailer where the wires and connections run in conduit aft with breaks for the black wire to drop down to the running lights to look at the wires, grounds and connections, and pulled and pushed on the connectors. Now all lights function as they should. So I suspect that that there is a short that back-feeds one wire to the other wire/s. I will run a new set of wires and that will hopefully solve the issue. Thanks for your input. It’s appreciated.

Iowaboy1, bigcrappie and basseyes thank you all for your great insights. Its appreciated.

2004 Tundra

Feeback voltage – never thought of that. When I do apply a load (connect the light to the brown wire) I read 0 volts at the splice before the light and inside the light. Unspliced I read 12+ v before the light.

So it might be on the truck side. I will check. I will also check the grounds but if the turn signal in the light works, all the other lights work and I can get 12v in the wire right before the splice to the light right before the light using the ground inside the light to check the brown wire, could it be a bad ground?

Would not one fuse energize all the lights on the trailer circuit? If so the rest of the lights work fine so it wouldn’t be a bad fuse; or so it seems.

When I tried a bulb with clips right from the truck-side connector (where I read 12+v) it would not light (that could be operator error as well so will re-check).

Using a buddy’s truck to check is a great idea.

Thanks for your input. I will report.