Brake &signal lights on drivers side rear malfunction when head lights on.1997chevy 2500ck
Most likely a ground issues with that side, you will have to remove the tail light assembly to check the grounds, if the grounds are good then ther are a know problem with the IC board in the tail light housing. Also check the bulbs, have seen a few that have cross circuited themselves causing all kinds of wired lighting problems. HTH
Or it is a switch. The headlights should not affect the brake lights as they are different circuits. It very well could be as Tennisshoes suggested, the tail light board or crossed wiring. Depending on the abuse a 2500 work truck has had, anything is possible as far as damage goes. Checked for lose or frayed wires that are rubbing together.
Search Chevrolet C/K 2500 Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Chevrolet C/K 2500 Experts