I got curious and wanted to test out the rear locker in an empty parking lot. For some reason, it will not engage. The dash light for the rear locker flashes red. I have read the manual and tried everything that I could think of. The center lock engages fine. Anyone else with this issue?

 

It may be because of driveline binding since you're on pavement.

Also make sure you're in 4LO and have the center differential locked.