Chevrolet Repair: 4x4 problems, shaft coupler, chevy 4x4

Question
Hello, Thanks for this free question answering website! I own a 1991 Chevy 4x4 350 5 spd ext cab and I am having problems with the 4 wheel drive. At first I noticed it was blowing the 4x4 fuse under the dash so I replaced the elecrical harness that GM recommends replacing. the harness that goes to the accuator solinoid on the front axle. It worked 1 time then never again. So I replaced the accuator solinoid on the front axle... nothing, rechecked (with a digital v. meter, continuity and voltage.) the replacement harness, it checked out o.k. tested  the wiring from the shifter on the floor to the front axle...

Answer
Hello Rick,
Normally, the problem in those trucks is the actuator.
The replacement wiring harness usually only comes with a replacement actuator that is different from the orriginal.
I will send a couple links about some stuff I have found on line, but have never personally tried. They sound like a good idea, but I have stayed stock for years, and am still running about six trucks in my fleet with the old style.

I assume you checked your fuse again after it quit again?

Here is how the power goes.
When the ignition switch is on, there is power to the 4X4 fuse. Power goes first to a switch on top of the transfer case. That switch is just about below the passengers seat, and if the truck has seen some rough 4X4'ing, I have seen the cross member under the transmission bent, and that switch kinda jammed up against the floor.

So..with power going to that switch, you shift the transfer case into four wheel drive. That closes that little switch, and sends power to the front axle actuator, and to the switch on the front differential for the 4X4 light. As the actuator expands, and engages the right front axle shaft coupler, it closes the light switch, and illuminates the 4X4 light.
I would check those switches, and especially their wires, and make sure one of them isn't shorted to ground.

Here are those links, and although they are very interesting, a couple statements are not 100 % accurate. But all in all, some good information.

http://www.4x4posi-lok.com/PDFs/troubleshootguide.pdf

http://offroadltd.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=ORL&Product_...

http://www.4x4posi-lok.com/

http://www.pirate4x4.com/welcome1.html

http://www.pirate4x4.com/tech/billavista/PR-shaft/index.html


Then go to this link, http://www.chevytalk.org/threads/showflat.php?Cat=0&Number=625259&an=0&page=0#62...

You will probably want to sign up there...it is free.

Van