I was asked to pull a boat the other day i was like no problem because well i have a 4wd so i started going up a hill on a gravel road and locked it in so i thought the 4X4 light came on the floor and i started taking off and all that was spinning was the rear wheels four wheel drive wasn't working but it said it was locked in but the front wheels weren't even trying to pull anyone have any ideas on how i can solve my problem i would appreciate it thanks.

 

Front differential 4x4 actuator. It's about $100