Fuse Box and tail lighting question

I'm tryin to figure out what the "room" fuse in the fuse box goes to? I'm having a tail light problem. The front signal lights work great but the tail lights are all AFU. I have 1 back up light that's always on and when I signal left, both tail light and signal lights blink very dim. On the other side the lights work good. just the left side. Please send me your ideas. Thanks.

Check your grounds. That what it sounds like.

check to see if anyone at some time installed a trailer harness or something to that nature. there may be some bare or short wires behind the taillight or under the bed.