THE ABOVE , put a ground on both tail lights if u don't have both of them grounded .
- Have to ask... you have checked all bulbs in question for function and type?
- Did things ever work correcrly?
- If yes what changed from thentering to now?
- Backup lights use a switch on column or console, switch could be bad.
- Brake lights use switch that pedal pushes on, seems to be working, one side dimmer than other does suggest ground or bad connection.
- Head lights but no tail lights or dash lights suggests headlight switch.
- You didn't talk about turn signal, working ok? Some circuts run through the turn signal switch and /or blinker, and /or flasher.
- Are your flashers working?
