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 1500 Tail Light Wiring in Cargo Area May be Damaged
Chevrolet Express 1500 Problem
Model Year Affected: 1999
Visitor, 1999 Chevrolet Express 1500, 150,000 mi
Bulb sockets corroded in both rear taillights causing issues with braking and tail lights when headlights turned on. When driving, lights indicate bright. When braking, lights dimmed. Just the opposite of what lights should indicate. replaced wiring harnesses on both sides. Problem solved.