It could be the fuse.
My Tail Lights And Dash Lights Don't Work In My 99 Honda Accord But My Brake Lights Work. What Could Be Wrong?
Taillights in honda civic won't work
I got the same problem, it was after a radio install. Ive been doing car audio for a long time and haven't seen this. I checked all the fuses and everything is fine. However, I noticed that the ilum and dimmer wires were twisted together, but they are inactive from the harness. I think is one of the relays but I'm not sure if its Light 1 or Light 2 in the fuse box under the hood.