Truck Started Cranking By Itself, key in the off position.

Yes- We've combed over both fuse boxes, we've searched high and low. We've actually found the target wire, but we haven't been able to locate the exact location of the breach. We know the problem is with the starter signal wire. There is a short to power between the starter signal wire and the ignition power supply wire. . . But, alas, as is so typical with Paccar, we're on an electrical hunt trying to find the exact source of the problem. It seems like it should be easy given what we know so far. It's not.

For the sake of time, we hope to bypass the ignition switch and install a starter push-button. Then we're tapping out on this quest and sending it off to Mark- the "electrical guru." We'll see what he comes up with.

This incident definitely took us by surprise. We were moments, if not seconds away from major catastrophy- it was ready to catch indeed. It was the end of the day; the tool shed was just locked-up, the tool truck just pulled away. Lucky there were channel locks in another truck parked nearby. It was quite a sight to behold: A chicken with it's head cut off at night, in the dark, trying to disconnect the smoking battery terminal with channel locks. . . And no gloves to boot!

Sorry to hear about your wife's Trail Blazer. What a nightmare! I can imagine the scene trying to locate a wrench! We're probably gonna put kill switches in and we're definitely gonna make sure there's an easy access wrench in each battery box, because, while it's rare, and "shouldn't" happen again, ya just never know!

Thanks so much for the reply, sorry for the delay getting back to you. Hope all is well.

Kind regards,
5UG

 

Yep- you're right on. We've replaced the ignition switch and checked over the other usual suspects, but the problem seems to be the starter signal wire. There is a short to power between the starter signal wire and the ignition power supply wire. We've not been able to find the exact source of the breach. We're handing it over to Mark, one of the local professionals with a niche for electrical. And I couldn't agree more regarding "Since it's a Paccar... Check the wiring harnesses." It's almost always a wiring issue with these trucks! Rarely does a part replacement cure the problem and/or code. Not that one should just throw parts at it, but you get a specific code, and it only points you in the right direction, it doesn't actually solve the riddle. Even with a good computer, there's still a great deal of process-of-elimination style, troubleshooting/problem solving involved. At least that's been our experience. Maybe we're doing wrong.
Hope that makes sense.

Thanks for the feedback- this was/is a real humdinger. This truck actually has a couple issues. I think we're close to solving the puzzle though. Hopefully Mark can figure out the last few pieces.

Fingers crossed.

Thanks again for your reply!

Kind regards,
5UG

 

That is the stuff nightmares are made of. Seriously. Dare I ask how it ended?

 

Update:
We buttoned everything back up at the ignition switch so we could bring the truck to Mark, (the hard to reach electric whisperer), tomorrow morning, and voila, everything seems fine. I think we're back to a solid state of function, but this truck has had us feeling a bit like we're in a game of Russian roulette. (Aside from this random cranking issue, it kept de-rating in the middle of loads due to an SCR issue for no good reason). We don't know the truck that well as it's new to us, and we didn't get off to a great start, but it looks like we were able work it out.

I think it's already been posted, but just in case:
It was a short to power to the starter signal wire. We never found the breach. We bypassed it with a push-button, and will be putting a kill-switch in for good measure. We don't anticipate any more cranking in the meantime, but, apparently, ya never know!

Thanks for all the feedback! Wish I could say the stories were a comfort, but, not so much. They were fun to read, and I appreciate the replies, but no comfort at all. Haha

Anyway, thanks again,
5UG

 

Wow, that was a lucky break- No pun intended!
Thanks for getting back to me on that. . . What a crazy situation.

 

I responded below, meant to include you in the reply so you know I've responded- still learning the forum controls. . .

Kind regards!
5UG