3406B coolant temp sensor location

Interesting. I haven't seen one like that before.

 

@wore out said that the power goes to the switch in the dash first. It looks like wire 242 provides the power from the fuse box, and it also provides power to other accessories. 242 should get its power from the fuse labeled "sw acc" which is the third fuse from the top on the right side of the fuse panel.

I would make sure that you get power there first, and then start chasing through the clutch switch and throttle switch. It seems it must go back into the cab to the level switch next to the jake switch (3 cyl vs 6), then to the jakes. First step get power to the jake on/off switch.

I have a pdf of the wiring schematic for 379s I can email to you if Peterbilt didn't give you one.

 

I went back and looked at the photo of your fuse panel: it should be the second fuse down from the top on the right on yours.

 

Try this.

 

Thats the fuel pump switch... there is not really any difference between the 2
There's a fair chance the clutch switch is either out of adjustment or bad that seems to happen often

 

He should have power at the dash switch though if the clutch switch is the problem.

 

I didn’t do too bad from memory lol but I am forgetting more and more circuit numbers. I also couldn’t remember that switched acc label either cause I tried lol. Anyway if that fuse doesn’t have power the power to it comes from key switch should be ign side. Since the switch is obviously working it may been left off at some point never tell with old equipment