Cmark said: Nope. Someone has bypassed an A/C pressure switch. View attachment 362287 Before you go chasing ghosts with your Can network, did you have the batteries isolated when you measured the resistance between pins 50 and 34? Click to expand... Always when someone shortcuts the system in these computer-controlled Cats, they cause a F##k up down the track. Back 2011 we had a 637G with an intermittently non-operating cushion hitch. The downtime hours & $$$$ spent, trying to isolate the fault over 6 months was unbelievable. I jumped on & drove it for a couple of hours. It worked 75-80% of the time. I told the owner I felt it was an intermittent electrical fault. I removed the panel on the front of the cab where the fuses were & found a wire, the operator had "hot-wired" into the system for a sound system. I disconnected it & ran the wire, fused, direct off a battery. The operator got a "tune up"! We should have "sent him down the road between two suitcases" Problem solved.