4WD not engaging

I got this truck from my father a yyear ago. While he owned it he had trouble maybe 100000 miles the 4wd would not dis engage. He had it pro serviced twice because they didn't get it the first time. Aprox 150000 it would not engage had it pro serviced (now he spent more on the training than the car is worth) had a new part installed forgot the name at the moment I want to say some pressure box or somthin like that. It stopped working again won't engage4wd, While I had it I noticed the wiresfrom the transfer case were severed and coroded, I addded wire to those and just twisted them together and taped them off, that didn't work. My trans went reverse and 2nd gear went so I replaced that with a junkyard one. Also had to replace the modual for the side of the transmission that affect the nuetral safety switch also had to replace the shifter cable. Since then ( now snowing allot and no garage, no job.) Since then I noticed one of the rubber tubes that goes from the transmission to the transfer case is just dangling down on the ground, I tied uit up for the time being. The 4wd hasn'T engaged for over three years now and I have no idea what it could be, is there any cheap way to get this working again or to at least find out what the problem could be? Also is there a way to overide it and engage the 4wd manually when I need it?