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i bought a 1993 gmc 1/2 ton pickup and i was driving it around in the snow in 4 wheel and then my 4wheel light on the floor flickered and then went out. now it won't go into 4 wheel at all. i've checked the transfer case and its fine so the only thing i can think of is it has to be what ever engages the front diff. any help would be appreciated.
 

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Not sure about your truck, but my 83 s10 Blazer uses a vacuum actuator to engage a cable that locks the front diff. If you lose vacuum, your hubs wont lock and the light goes off. There is a vacuum line that goes from the engine to a switch on the transfer case, and then to this vacuum actuator, which is on the fenderwhell. Check all these vacuum lines for leaks.
 

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Your 93 p/u uses a electro-thermal actuator, and they are prone to failure. It screws into the axle, and has a two wire harness that plugs in at a connector clipped to the back side of the rh axle tube on the front axle. The connector is grey. There is a white connector beside it, this is for the switch that turns on the 4WD indicator on your shift console. IIRC, the actuator has a 1 1/4 hex on it. I'd remove it, and test it before you buy a new one. They are not inexpensive, around $100.00 CAD. You can test it with some jumper leads and a battery. If it extends when the two leads arehood to 12v, it is good. If it does not, it is no good.


If this is good, look for power dom the wires that connect to the actuator. With the key on, tranfer case in 4WD, ther should be 12v across the pins on the connector. If there is not, look to see if the 25 amp 4WD fuse is burnt. If it is, replace it, and see if it blows again. If so, there is a shorted wire between the transfer case switch and the front axle actuator, another common issue with these trucks.
 

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Aftermarket option

There is a kit that can be purchased that eliminates the vacuum setup and converts you to a cull-tilt cable setup and also another to go to manual hubs. Try a local off-road shop, it really should not be more than $200.00.
 
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