I have a 97 SR5 with original factory locker (rear). The unit has always performed flawlessly until last week. When I engage the locker switch, the Diff Lock light flashes on the dash but the locker never engages and the light never switches to solid. I've tried all variations of engaging it, have tried speeding up, slowing down, turning at acute angles, and going over some serious bumps to try to get it to engage--no luck.

Any thoughts on how to diagnose the problem?

Thanks

George