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Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3362
Experience:  ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician
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02 379 ac relay control wiring issues. Cross 30 and 87 on

Customer Question

02 379 ac relay control wiring issues. Cross 30 and 87 on the ac clutch relay and all works great. Key on, I have ign feed to 85 or 86, no ground to the opposite term.
Submitted: 2 years ago.
Category: Medium and Heavy Trucks
Expert:  Jeremy replied 2 years ago.

My name is ***** ***** I will assist you.

Have you tested the high and low pressure switches as well as the a/c clutch? Those grounds go to those locations.

Go HERE for needed diagrams.

Peterbilt doesn't have good diagrams for that year of truck outside of the dealer network.

How the system works, it usually grounds out to the head unit, then to the low pressure, then hig pressure, then clutch, then to starter/body. If you jumo the relay and the system works, then the pins just need to have a ground added.

You can chase and find the ground attached to the body, but it will be some chasing.

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Customer: replied 2 years ago.

The AC relay is part of a miserable fuse box to remove and connect a "foreign" ground to the respectable terminal 85 or 86 of that relay. The power to 85 or 86, is the issue. According to wiring diagrams i received from peterbilt since my experiance started on this website, appears to be "piggy backed" to terminal 30 of the relay.

Expert:  Jeremy replied 2 years ago.

Why was it piggybacked? Did the power get lost there before? Sounds like a difficult rewire is on your hands.