871 jakes and power issues

[kmk]

Check the connections to the cab computer, it is located behind a kick panel on the driver's side. Focus on connector J5(1605) pin F8 is for the engine brake, I think. No corrosion whatsoever on the pins or inside the connector or wiring, any small amount of additional resistance will make the controller act up. Water intrusion can destroy things really fast there too. However it sounds like you have other more serious issues. Just follow what the rest of the guys are recommending. Don't put any test light or probes there, I just saw our company mechanic fry one of these things with a power probe.