check the FSM sticky'd at the top of the forum, it has all the schematics and info for the AC. I converted my AC last summer, and I dont remember any switches or wires under the hood except for the compressor clutch wire. inside the cooling unit under the dash may have a switch. Are you converting to R134a when you put it in? itd probably be cheaper if you dont have any access to R12. Good luck!

'94 X-Cab, EB inside and a few fabbed parts. My wife: "How about you stay on the road?" Me: "I drive a Toyota truck, the road is OPTIONAL!"