98 F150 transfercase will not engage
 

Guys, I have a 1998 F150 with the 4.6 auto and 138,000. I went to put it into 4Hi and the trasnfercase is not engaging. This truck has the manual transfercase shifter on the floor, not one of the turn the switch on the dash type engagment systems. I did manage to get the transfercase into neutral (a lot of good that did me) and back into 2Hi but no 4wheel drive. What steps shpould I take to troubleshoot this? No light on the dash, nothing. I'm not familiar with the transfer case (don't even know what kind it is) so any guidance I can get would be greatly appreciated.
George