I own a '94 Full size. It has a floor shifter. Whenever I shift into 4lo, 4hi, it engages in the transfer case but will not lock in up front. I also noticed the 4wd light is not coming on. Someone please help!! It Will be appreciated.

 

I would suggest crawling under the truck and tracing the vacuum lines. They could be cracked, torn, ripped off ect causing it not to work. That reason is why I prefer an older real full size with manual locking hubs haha.

 

yep my guess too a bad vacuum line

 

My guess as well -- vacuum line. I'd replace any that look or feel questionable.

 

Thanks!! Ill check it out in the morning.

 

My 92 full size has a electrical actuator it is about 100 bucks! if this is your problem check out 4x4posilock they make a cable kit that replaces this actuator. The actuators were know to go out.