Rear Diff Light Turns on at 80 mph

Great. Thanks. I saw the explination above on how to engage so that helps.

So it stops blinking when engaged? And the color is always Red for the rear diff?

 

Update on OP: the issue didn't happen again until I used the highway 3 weeks later. After that trip I think I unintentionally fixed it by using 4Lo and the locker when off roading.

I just bought this truck so I wonder if those functions were never used and the sensors were dried out. I know the owners manual recommends driving 10 miles in 4wd per month.