My sons 93 F150 won't engage in 4 high but will in 4 low it's auto 6 cyl

 

I had a 95 with a straight six in it and a manual shift 4x4. First does the light come on the dash for 4x4? if not then there is somethin up in the t case probably. The shifter stripped out in mine and I had to go underneath it and engage it by had. But if it is engaging in 4 low then prothe lever is probably fine. I would guess that there is something going on in the tcase those were the borg warner 1356 tcases and they arent to expensive. Also make sure that when you shift it into 4 low that it is actually in 4 low and the light isnt just on.