Just bought a 2006 f150 with 5.4 triton the 4x4 seems to work then not work.. it's a manual shift for the 4x4.. the doesn't come on.. but lights up when you first start the truck.. any ideas?

 

There is a switch in transfer case that turns on the 4x4 light. It's probably failing. The ECU runs through a lamp function test upon start-up, so you know the bulb is good. I bet the 4WD is actually working.To test it just stop in some loose dirt or gravel, put the truck in 4 high and jump on the throttle. If only the rears spin, you have a problem. If its working, the truck will accelerate rapidly with little or no wheel spin.