C15 jake not working

If not working at all I'd say start with clutch switch. Does your cruise control work ?

 

Your clutch switch will be fine then, does the engine brake work on any stages or nothing at all ?

 

You have to have it connected to a computer to check all the switches that control the Jake's ability to activate There is the Idle validation switch, also you can manually activate the different solinoids and with a bar on the valve cover hear them. The switch itself could be bad, the clutch switch. All will show up with it hooked up.
Just a thought!

 

and it could be the vva and injector wiring harness which also hooks to the jakes about 185 each, theres 2 of em on the c15

 

If you've recently had your valve covers removed, maybe when they were put back on the wires to the solenoids were pinched.
Do you have any codes flashing on the dash!?

Cheers,

 

If your handy with tools, take the rocker covers off and check if the cat brake solenoid plugs are still in. If they stopped working not long after the recent work you mentioned then this could be the problem. If it's not the problem it could be a switch and a laptop will find it easy.

 

a whole lot of actuators get replaced, I think the problem may be the wiring harness instead in a lot of cases