How do you find out why a 94 GMC Z71 will not go into four wheel drive?

Answer 1

There are a number of reasons these don't work. TAke it to a garage.

All the four wheel drive trucks that have the lever on the floor like the 94 have a solinoid that acctuates the front diff. There is an update for them that convert themt from an heat based solinoid to an actual electric solinoid. If you call the dealer and give vin he can tell you about the update.