1999 Peterbuilt 379 No Jake and No Cruise

Wiring harness from computer to jakes. You have signals from switch to computer do you have it from computer to solenoids or switches under valve covers?

 

Wouldn't the solenoids be tied in to the wiring completing the circuit?

Hard for the ecm to say yes if the circuit isn't complete.

 

Did the Jake brake and cruise just stop working together at the same time or at different times?

Was this an intermittent issue before this started?

Has the truck had any tuning work performed on the ECM lately?

What motor is in the truck? CAT C15 6NZ? Cummins N14? Detroit Series 60 12.7?

Have you removed the rocker cover(s) and inspected the wiring to the Jake solenoids? Have you ohmed the Jake solenoids to verify that they are good?

I would set up my DVOM at the Jake solenoids and operate the switches to verify that the signal is reaching the Jake solenoids or not and if it is not then work backwards in the wiring diagram.

Something in the circuit is not working properly and it shouldn't be hard to identify if you verify the wiring in segments.

 

Floor mat up under throttle pedal ?