The tail light wiring harness in the cargo area is not protected very well. As a result it may become damaged due to normal wear a tear. This damage can causing some or all of the rear lights to stop working.
Car Problem Reports
Chevrolet Express 3500 Tail Light Wiring in Cargo Area May be Damaged
Chevrolet Express 3500 Problem
Average Mileage: 116,216 mi (80,000 mi - 168,950 mi)
Visitor, 1997 Chevrolet Express 3500, 80,000 mi
Tail lights and blinkers started to malfunction. Problem was a bad ground and fixed by running additional ground wires from light sockets to frame.
Visitor, 2001 Chevrolet Express 3500, 168,950 mi
tail lights not working when night lights are on.
Brake lights work fine when the running lights are not on, butonly the top brake light works when the running lights are turned on.
Visitor, 2001 Chevrolet Express 3500, 99,700 mi
brake lights work fin till you turn on headlights then they do dim only to leave third brake light