I have a Dodge 3500...when I step on the brake pedal, the front parking lights, roof lights and the clearance lights on one dually fender light up.
Check for a crossconnected bulb in the rear first, sometimes a filament will break off and fuse with the other filament in the bulb, if you don't find one then start tracing down grounds for the lighting system, could be a bad socket or wire.
Search Maintenance & Repair Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Maintenance & Repair Experts