Loi, here is what I found "SYSTEM OPERATION
When ride height decreases due to weight being added to vehicle, height sensor arm assembly rotates upward in relation to height sensor. See Fig. 1 . This activates a timing circuit in height sensor. After a delay of about 13-27 seconds, height sensor grounds ELC relay, turning on compressor. Air is then pumped into struts, raising vehicle. Delay prevents system from operating during normal changes in ride height that occur during driving. As vehicle rises, height sensor rotates downward. When vehicle rises to within one inch (25.4 mm) of curb height, height sensor opens ground circuit to ELC relay, turning compressor off.
When ride height increases due to weight being removed from vehicle, height sensor arm assembly rotates downward. This activates the timing circuit in height sensor. After a delay of about 13-27 seconds, height sensor grounds exhaust solenoid valve circuit, causing air to be vented from struts, lowering vehicle. When vehicle has lowered to within one inch (25.4 mm) of curb height, height sensor opens exhaust solenoid valve circuit, causing exhaust solenoid valve to close." from here. Also check it for more information on the ride height system. It is compressor controlled, like an air ride system :-) Hope this helps to get you started.
Here is a great shot of where it is located. Picture is taken from behind the Right Rear Wheel and great information about it on here