The car has been driving great since changing the throttle body. I also changed all the fluids and filters so now is a good time to address the wiring issue.

The tail lights are such a mess.

This is the right side.
Black and white wire is cut off, I guess it's no longer needed with the new tail lights. Brown is ground, I opened it for testing.
Black wire is the one that's spliced to bring power to the left tail light.
You can see on the left side how the wire that's been spliced on the right side comes to give power to the left side.

The black wire on left side is cut off and I'm thinking because it probably doesn't have any power.
I tested it with a multimeter and there's nothing, while the same black wire on the right has voltage.
Wherever this black wire is coming from, it lost power somewhere.