Help! Red 4wd light flashing - 4wd won't engage

Monday my wife picked up my truck from the detailer. This morning I got in to drive it to work and noticed that the red 4wd light was flashing. I called my wife and she tells me that the light was flashing when she picked up the truck but she forgot to tell me. I switched it from 2wd to 4H and could hear the switch, the indicator came on (along with the red flashing indicator), but it didn't engage. I pulled over and stopped, and switched it to 4L. Indicator lights (including ABS) but still no engagement. WTF!? Any Ideas before I make the trip back to the detailer? Am I risking damage by driving it this way? (No strange noises - just the flashing red light)

There were no issues prior to detailing, is there something that he could have unplugged, broken, etc?

 

Your locker button is On

 

I think the red flashing indicator is the Rear differential lock.
Check the switch on the dash.
It shouldn't have caused any damage, it will only engage in 4 Low

 

Problem solved. Thanks guys!

 

LMFAO. I've been spending the last hour trying to figure this out. Just put a Magnaflow on, as well as first oil change after seafoam treatment. Driveline light was flashing, rear diff button depressed, relieved!

 

Zactly!