ac compressor connection question(s)

[rodstored-72]

all,
i have a vintage air "universal" ac system installed in my 1972 chevy truck. i am running a 350 (383) with a '92 p/u serp. belt system. my r4 "disk" compressor has 2 wires running (white & blue) from it. i am installing a holley throttle solenoid to adjust the idle when the compressor kicks on.
i want to know what wire is the "kick on" wire that i need to connect to so the solenoid will operate at the right time?
i believe that it needs to be the power wire, but i am not sure....

thanks for any input from you guys!!!

rodstored-72