I have a 2000 F-150 4x4 and the four wheel drive isn't working properly.

It does work,but to get it to engage I had to drive in reverse for a couple feet then it locked it and everything was fine,pretty sure that isn't normal. Any ideas on what could be wrong with it? As soon as I turn the **** it lights up on the dash,but the front tires don't spin.

 

The last link in the train is the coupling sleeve engaged by the front actuator on the axle.
It locks togather the front drive.
Look there for the issue.
Good luck.