1995 Peterbilt 379 Jakes Not Working

1995 with a 12.7 - but all my problems with the circuit were from ground wires being tapped into.

Not a mechanic, but I believe the circuit of clutch/brake/cruise etc all run a ground circuit to activate/deactivate.

Check any wiring that they may have tapped into in the engine bay to source a ground.

 

Mine was pretty original too - it was something like an old ELD unit that I pulled (was a DOD truck) that triggered it. Or a cigarette lighter, something dumb.

If this just occurred after the out of frame, I’d be having them run through any wiring alterations they made while you’re there, to track it down.

If everything else clutch/brake/bump/cruise are working - it’s somewhere else.

 

Well if you think it’s switch….do what us poor folks do….go to Napa get switch(or comparable part…put it in
If it worx keep it
If not you know it’s not the switch….put back in box…return to Napa
Rinse&repeat
Good luck

 

One side of the switch goes to chassis ground, other side comes from ECM, so that when switch is on wires from the ECM see ground.

Since it was just overhauled I would double check that both the wires are tight on all the jake solenoids under the valve covers. I see the spade ends on the wires loosen up quite often and need replacing.


Wiring diagram for the jake switches goes something like this:

ECM
| | (2 wires from ECM to range switch,
| | one for low, one for med, both see ground for high.)
| |
low/med/high switch
|
|
|
on/off switch
|
|
|
Ground