95 GMC Sierra 4x4 problems....

I have a 95 GMC that has a issue with it's 4x4 system. The truck runs as if it is constantly engaged in 4wheel even though the shift is in 2wheel. I was told it might be the actuator, so i bought a new one and installed it, but that didn't seem to do anything. I took the old actuator and new actuator and "plugged" them into my 98 Chevy Silverado, pushed the button from 2 into 4Hi and 4Lo and presto the actuator works no problem. So then I guessed it must be electrical on the GMC Sierra.

I tested the connection at where it plugs into the actuator (on the GMC) and it states that there is power going to the plug. I was told it might be the switch on the transfercase that is causing the problem...is this true?

If so, where is the switch located, what is it called and is it easy to repair?

Thank you.


More detailed info if it helps:
When the actuator was in the GMC, like I said it was in constant 4Hi and wouldn't release back into 2. Underneath the truck, when I took out the actuator the "pin" was in the out position and we couldn't push it back in, put it on the Silverado and it "reset" so the pin went back in. Well when we put it back in the GMC it drove like it should and then trhough itself into 4hi...even though the shifter was in 2wheel. But now when we took out the actuator again, reset it and put it back into the GMC it doesn't do anything, you shift to 4hi or 4lo and it is now in constant 2wheel drive.

I hope this helps or makes sense. The dealer here has no clue, a 4x4 experts here (so called) have no idea. I am desperate and need help.

Thank you.

What type actuators do you have? Are they metal or plastic? I'm assuming- I don't know what to assume other than the switch in the transfercase is where I'd look. If there is a BROWN wire at the actuator plug(should definitely be one on the 98) it should have power anytime the key is on. If nothing else, I'd put a switch in the circuit that feeds the 12v to engage the front axle actuator to be able to manually control it(its a light blue wire on a 96)

On some GM trucks, there is a vacuum switch on the transfer case that has three or four small vaccum lines going to it. Not too expensive and easy to replace. Just so you know, there may be a round red metal tag on the transfer case with a number on it , eg. 242, or 231, etc. Not sure off the top of my head, but you may need to know this. It doesn't hurt for future reference....

What type actuators do you have? Are they metal or plastic? I'm assuming- I don't know what to assume other than the switch in the transfercase is where I'd look. If there is a BROWN wire at the actuator plug(should definitely be one on the 98) it should have power anytime the key is on. If nothing else, I'd put a switch in the circuit that feeds the 12v to engage the front axle actuator to be able to manually control it(its a light blue wire on a 96)


The actuator I have is plastic (not a big fan of plastic). And the wiring to the "plug" does have a brown wire. the GMC used to have the old actuator kit (metal) on the truck, it broke before I got it and was replaced with the new 98 actuator kit.

Thank you for the tips! This really helps.

On some GM trucks, there is a vacuum switch on the transfer case that has three or four small vaccum lines going to it. Not too expensive and easy to replace. Just so you know, there may be a round red metal tag on the transfer case with a number on it , eg. 242, or 231, etc. Not sure off the top of my head, but you may need to know this. It doesn't hurt for future reference....


Sorry for the delay in replying as I have been out of town. I want to thank you for the tips you gave me and will check into the vacuum switch on the transfer case. This really helps me a lot and gives me some place to start.

This site is fantastic, much more helpful information then the damn mechanics here in town!! Thank you all for your help.