Well, I Have a 1997 f150, and the 4wd (high and low) won't engage, any ideas on what it could be and what I should check?

 

do you get either the Hi-Lo or the 4x4 light on the dash ? Do you hear anything when you switch the **** ? Two things happen... one is an electric motor on the transfer case switches HI-LO if needed... second is a vacuum cylinder on the front axle engages the axles to the driveshaft with a pin.