The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - How do I wire a pressure switch and relay

fixit-p · 05-31-2009, 04:35 PM

Whether you use the press. sw. or toggle sw. to turn on your compressor a relay is a must imo. The relay can handle more current than either switch and simplifies wiring.

I would connect terminal 30 of the relay to batt or better yet the alt. buss terminal. Term 87 goes to the compressor. Terminals 85 and 86 are used for the control circuit I always use 85 for ground, run it to the nc terminal on the pressure sw and the common terminal to ground. Terminal 86 goes to power either ign or batt depending on when you want the comp to come on.

05-31-2009, 04:35 PM	#2
fixit-p Registered User Join Date: Dec 2008 Location: Yay Area CA Posts: 2,329	Re: How do I wire a pressure switch and relay Whether you use the press. sw. or toggle sw. to turn on your compressor a relay is a must imo. The relay can handle more current than either switch and simplifies wiring. I would connect terminal 30 of the relay to batt or better yet the alt. buss terminal. Term 87 goes to the compressor. Terminals 85 and 86 are used for the control circuit I always use 85 for ground, run it to the nc terminal on the pressure sw and the common terminal to ground. Terminal 86 goes to power either ign or batt depending on when you want the comp to come on.