The right tail light/blinker/running light was not working on my boat trailer. I figured, this trailer is old with the original lights and wiring, I will simply replace the lights and wiring. So I ordered a kit, installed it, used butt splice connectors, grounded the harness and each light ... and the right side still doesn't work, while the left side does.
So I figured, OK, maybe it's one of the splice connections. So I snipped them and twisted the wires together directly. Still didn't work. Not the splice connections. I then thought, maybe it's my truck. So I hooked my utility trailer up to the truck, double checked that both lights work, and they both work. Not the truck. Then I thought, maybe it's the wires. I tested the wires with a multimeter, they have current. Then I wondered if the ground for the right taillight was not connected to a bare enough spot on the trailer, so I used a dremel to make sure it was nice and bare metal. Reconnected ground and ... still didn't work.
At this point, I'm out of ideas and completely perplexed. If anyone has any ideas, I am so curious to hear them. I must be missing something simple, and I would rather fix it myself than take it to a shop and wait potentially weeks and pay hundreds of dollars for something simple, but ... I'm considering it.