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Post by yjsaabman on Mar 15, 2007 17:59:10 GMT -5
The 4WD indicator switch is located on the front axle vacuum actuator. It is an electric switch that essentially tells you if the vacuum disconnect system is engaging. The movement of the vacuum actuator is what closes the switch. Problems are usually vacuum related.
A hand held vacuum pump is the best tool for diagnosing this system. Make sure you use the brake bleeding catchcan, though. I sucked a good bit of nasty water out of my front axle actuator. Use the vac pump to check the diaphram in the actuator, the vac lines running to the vac switch on the t-case, etc. I did all of this while swapping trannies, so accessability was much better, but you can get to everythingwithout too much hassle. It's even easier if you drop the pan and lower the rear of the driveline a few inches.
The vac switch on the t-case has a block of 4 vac lines that plugs into it. Two of these go forward to the actuator (one for engagement, one for disengagement) and the other two are manifold vacuum source. The plug is indexed to pins, so you can only put it back on one way. Put silicone down in between the pins on the switch to avoid it clogging the lines, and apply some silicone around the bases of the pins on the actuator before re-connecting to prevent leakage.
I checked everything before taking it down off the jack stands by running it in 4WD and checking to make sure all the wheels turned and the light came on.
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