how do i trouble shoot thermal 4wd actuator on 90 gmc half ton floor shift , truck engages 4wd intermittently dont want to buy an actuator til' i know its bad , do they get weak or do they just quit? transfer case is engaging,what sends the juice to the actuator? this truck has to get me through the winter while i let you guys get the bugs out of the LLY!!

John...The actuator gets its power from a switch on the top of the transfer case that closes when its in four wheel drive, Man, its been along time since I have worked on one of those so bear with me. IIRC there is a purple wire at the actuator, or maybe its brown. anyways, one is a ground(black) and the other is the power wire. pull the lever into 4x4 and use a test light and see if you have power to it, if you do, actuator is likely cause, when you update the actuator, there is a harness that must be used along with it..IIRC hoot had some pics of this...

Here's a link to Hoot's very well documented install. http://www.uscom.com/~hoot/cars/actuator_upgrade/GM_TRUCK_4X4_ACTUATOR_UPGRADE.html