Chosen Solution
My reverse lights, brake lightand turn signals do not work. Running lights do. My 3rd brake light(on the cab) does work though. Fuses are good, relay seems good, new tail light bulbs and circuit boards still no fix.
Id try the grounds remove and clean til u get bare metal even if they look ok. Try reinstall. Any recent work or damage to rear or bed of truck. Perhaps a nicked or overlooked connection.
Check your ground wires by rear bulb sockets. Remove grounds clean contacts with light sanding replace. Try relay to. May seem good but is not. Swap relays around. Must be equivalent size ok ?
