Can anyone tell me how to test the rear air leveling compressor to ensure it is working?

1. How do I cycle it to test that it even comes on?

2. If it comes on, how can I test to make sure it is providing enough pressure to raise the car?

3. Is there a fuse or switch for it?

I will ocassionally hear a running motor sound coming from the rear of the car which I thought was the fuel pump when I first turn the key. I do not hear the noise all the time just somtimes. My car is a 96 SLS and I replaced the front electronic strust with passive struts and I am geting ready to replace the rear shocks. (purchased complete set from Arnott's). Any input would be helpful.

Have one or two freinds sit in the trunk. You should hear the compressor run and see the rear end rise as the compressor pumps up the rear shocks. The switch is on the compressor and is activated by a control arm attached to the body somewhere near the rear axle. I'm sure there is a fuse for it.

Does the car need to be running or just the key turn on?

just key in and turned to the on position.

Tell me if this is correct:
If the key is in the on position while parked and I load the trunk, the rear shocks should adjust. If I leave the key on and unload the trunk, will it adjust again?

If you turn the key on it will run the compressor for a second to test it and make sure it's working. If you load the trunk with the key on it should start running to level itself. When you unload the trunk it will activate the exhaust valve and let air out. There is a relay center with a relay that turns the pump on and off. It's attached to the back of the rear seat and you have to remove the carpeted fiberglass wall of the trunk to get to it.