Okay, here's my issue. 2001 ram 1500 4x4. Aftermarket LED taillights. Headlights work fine, taillights were working as follows. driver side everything worked. passenger side tail light did not work, but turn signal and brake did.....sometimes. I got under there and wiggled some wires and got everything working like it should. That led me to believe I had a loose connection somewhere in the wiring under the rear end. Today I get under the truck and cut out the trailer pigtail, and also cut out the working that was going to a harness for a 5th wheel that the previous owner had installed. Now I'm looking at the brown/green going to the passenger side or right side, and yellow-white going to the left. I couldn't make heads or tales of the wiring diagram in the Haynes manual, so I experimented with twisting wires together, I blew a fuse lol. I replaced it, then proceeded to check every fuse in the box inside the cab and also checked most of the fuses under the hood. I also swapped relays with the blower motor relay because they were the same.
After that mess and out of frustration I decided to re-wire the 5th wheel hitch back into place (temporarily with wire nuts, when finished everything will have butt connectors and heat shrink tube.).
I have now proceeded to remove the switch and see if I could find a loose wire there. so far nothing. I'm currently looking at absolutely nothing working on the right side, and only getting the brake and turn signal to work on the left side. I'm so frustrated I've gotten to the point I started throwing things and cussing up a storm. I really need some help!
For some reason it cropped some of the pics kind funny. Will try and get better pics if needed.

I've attached some pics of the wiring as it currently sits, as well as a crack in the wiring harness......not sure if that's a problem or not. at thing point, I'm wondering if its the switch or something else. I checked for power at the 4 prongs in that harness. with one probe in the ground and the other on the leads, I never got near 12 volts. best I got on one prong was 7 volts.



the after market tail light


one of the two wiring harnesses tucked in behind the tail light




my temporary wiring connection. the loose leads went to the 4-flat trailer harness I need to re-install when I fix this issue.

 

Start checking continuity between the point where the trailer harness is spliced in and where the wire comes out the back for the connector. It could also be a broken wire inside the insulation. If you're able to move a wire and it starts working then it's usually a broken connection in the wire or connector at the end.

An easy way of ruling out the wiring harness from the front of the truck is to have someone apply the brakes while you use either a multi-meter or a test light to probe each of the wires at the spot where the trailer harness is tied in. If you get power or ground, I believe the later years are ground activated(?), then you know that the problem is between the trailer harness junction and the tail light plugs.

Relay [--------------------------------------] trailer harness splice [--------------------------------------] tail light plugs
Test your power here ^ (Then test the wires here for breaks using a multi-meter ^)

Hopefully that makes sense.

 

You definitely need to go over the wiring again. Looks like a lot of hack work was done. Also make sure you have a good ground at the tail lights. You will need to replace your flasher to a electronic flasher or the new led lights will cause the turn signals to stay lit(not flash).