But the four wheel drive doesn't work and the trans is making a whining noise when I let off the gas. The indicator lights on the dash won't come on when the tranfer case is in 4x4. 4 low work, but 4 high does not. I've been told that the "actuator"(vaccum module on back of front axle-dealer exclusive $273 part-) may be the problem. Is this diagnosis correct, before I blow 273 bucks on a tiny part?

you was told right ,you can start the engine and check the vacuum on the line going to the actuator for it,one line will have vacuum on it in 2 wheel drive and the other will have vacuum in 4 wheel drive,its best to test this though with the engine running,and you also have a vacuum switch on the transfer case that if it goes out it wont send vacuum to the actuator,9 times out of ten though its the actuator that goes bad, make sure the lines aren't bad also,if they loose vacuum it wont kick it in 4 wheel drive either,and yes it is an expensive part,i have replaced a few of them,good luck on it.

check the vacuum to the disconnect motor before replacing it. a vacuum leak will stop it from working. there are 2 lines. with the engine running you will have vacuum on one line in 2 wheel drive, and vacuum on the other line in 4 wheel drive. if you don't, check the vacuum switch on the transfer case. if it is ok, check for engine vacuum at the switch. you can also test the disconnect itself with a vacuum pump. be careful of the 4 7/16 bolts that hold the disconnect to the axle. the bolts are tining and they break very easy.