When i click the 4x4 High, I here the clicking sound but the 4x4 doesn;t engage.

What should i look for?

 

Does the 4HI light blink, or does it just stay in 2HI?

I had problems with mine too. First it wouldn't stay in 4x, which ended up being a bad/old vacuum line under the hood. Second problem was it would switch to 4HI, but the bulb was burnt out behind the button, so it would just not light up.

 

yes the 4x4 light does turn on on the button

 

pull your vacuum switch from on top of your transfer case (three tube connector pops off)
unscrew switch, take lock-deicer spray in all three tubes of switch while at the same time depressing the steel ball which will open all the ports, soak that baby, shake it all out, replace in case, put dielectric grease on the tubes (little bit) and replace three tube
connector, start truck, engage 4x4 and if it doesn't work remove gas cap, install match, engage running shoes.