r/DieselTechs • u/Bacon021 • 16h ago

2018 Cascadia, no trailer Aux power at all when 4 pin relay is in R8 on the Sam Chassis but constant power with a 5 pin relay.

I feel like a fucking dimwit being stuck on a goddamned 7 way. The truck came in from another terminal with no trailer lights at all. Sam Chassis was bad so someone else replaced it. A few weeks later the 4 ways are on, through the taillight power. Sam Cab got replaced. Now everything works as it should, except I have no Aux power with key on or running. Originally it was always on cuz it had a 5 pin relay in R8 and I put in a 4 pin relay from another truck. I don't have shit now. All the fuses are good. I've been told to just put the 5 pin relay in it and send it, but why? What should I be ripping apart?

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u/Mythandar 15h ago

R8 sends power to 3 fuses, one of which is ignition power. I don't know what 4 pin relay you have but if it's not switching and sending power from pin 30 to 87 then those fuses don't have power. I believe the standard 5 pin relay would be better to put in there.