I am in the middle of setting up on board air for my truck and i have a pressure switch to turn the compressor on and off depending on the pressure in the tank. the pressure switch is powered via a relay that is triggered by a key on wire. I have all the wiring done up to the pressure switch so all that is left is to hook up the compressor to the switch. when the key is off the switch does not complete the circuit and when the key is on there is 12V all the way across it (this is all with no pressure in the tank). my problem is that when i hook up the compressor to the switch and turn it on the voltage drops to 0. i dont know much about electrical circuits so any help would be good. is the compressor drawing too many amps or something for the switch to handle?

PS: the compressor works when hooked up to a cigarette lighter with the same ground.