Peterbilt 379 Cruise not working

I don’t know how to answer that.
All I know is there is a valve located right under your foot pedal. For me that valve was the cause of intermittent cruise and Jake working/not working.

 

Go back to the wiring schematic posted in this section. Wire 953 is a common wire to the clutch, brake & cruise control switches. Look for a brake pressure switch that has that # wire.

 

The brake switch is a ground circuit, there should be no power there.
It is normally closed so in the "normal" position it should have continuity.
When the brakes are applied it will go open.
You should be able to take your multimeter and unplug the switch and verify one side (wire 953) has ground. Then hook the multimeter to the switch and verify it operates as above. Next step is to verify ECM is getting the signal by using a multimeter on the ecm (wire 543 G2).
Trans should have 2 speed sensors, one for the ECM and one for the speedo. Some have one sensor with twin plugs on it.
Fastest way is to get someone with a laptop hooked onto it and they can see what inputs are working.

 

Whats the harm in trying?

 

If all the switches looked good to him all that's left is the speed sensor circuit as it cant be read when parked.