Ok so my last post was confusing. So here's a new one. My brakes is separated from the trunk. So there's taillight lights (on trunk) next to backup light. it usually lights up when I turn my lights when I drive. But when I was changing all the lights at the rear. Everything turns on but one taillight. The left turns on, but the other is not. The bulb is new. I don't know if its the connecter or wires.

 

Sounds like you are replacing the Accord's tail lights from inside the trunk, like this...



Please confirm. From your other thread, I see you have a 2005 Accord, similar to my 2004.

When you were changing all the lights at the rear, what type of bulbs are new? LED or incandescent? If they are LED, you may need to rotate the bulb 180 degrees or a half turn and then re-plug into the socket. Unlike incandescent bulbs, LEDs may fit in the socket either way but only operate one way.

If the new bulbs are not LED, there are other possible explanations. Eliminating some of them should help focus on the issue.