97 Expedition EB won't go into 4L.

5.4L, don't know which tranny, though it probably doesn't matter, 210K. It will switch between 2WD, A4WD, and 4H as it should, but won't go into 4L. I have had it in neutral with my foot on the brake and it won't go in. I've tried driving slowly and it still didn't go in. Could the transfer case motor going bad cause this, or is it likely the switch? Can't complain for the $900 I paid for it, but if its an easy fix or I'm likely to lose 4WD altogether I'll fix it.

Found the problem a while back, but I forgot to post the fix. The wiring to my transmission position sensor was messed up, previously fixed but left to rub on the front driveshaft. With the wires fixed I have 4L, backup lights, and it starts with the key (I had a starter button rigged up to the aftermarket remote start wiring).