Here is what I'm trying to do:
I have a 12v compressor typically used for an air horn vented to 3.5 psi actuating my VDI by a manual switch. I still have the wiring for the VDI solenoid (White connector) I read in the FSM that when the ecu tries to activate the VDI solenoid, it drops the voltage to the connector from 12v to less than 2v.

I'm trying to either find an electrical component that will switch the compressors circuit on when the voltage from the ecu drops below 2v. Or build one. From what I gather I'll have to use a transistor, but alas I am retarded and can't even figure out simple electronics.

Can anyone here help with this? I'm really stuck here.