TwistedMinis
+1y
Posting the same question 10 times is going to get you no where. It tends to piss people off around here, and then you don't get an answer. I would go delete the other threads since this one has some activity now.
Anyways, to answer your question... The pressure switch, depending on the one you buy will turn on or off at two pressures. When it turns on, it clicks the relay on. The relay has a power wire coming from the battery to it, and on the other side it goes to the compressor. When the PS completes the circuit, power is allowed to travel through the relay to the compressor to turn it on.