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

Hello- (again)!

I've got another question about a Paccar, although I don't think the engine type matters here.
I was at the yard working on another truck, when out of the blue, the Paccar starts to crank! The truck never turned on, just kept cranking. The key WAS in the ignition, in the OFF position. The truck continued to crank, even after I pulled the key out!!
I disconnected the battery to disable the truck.
It was a cool, breezy, rainy day. Not sure whether that matters.

Where do I start? (No pun intended.)

Any ideas?

 

Thank you! It is not equipped to top off low batteries or warm the engine on it's own.
I'll check at the starter solenoid per your suggestion. . . That's where my mind went too. Thanks again, I'm just scratchin' my head about what initiated the random, impromptu cranking.

In any case,
Kind regards

 

Thanks for the reply!
I can only imagine the expression on your face when that happened! Probably looked something like mine this evening. It was already getting dark outside when I was tinking around with the lights on the other truck. I'll have to crawl under and take a good look at everything during daylight. . . I'll be sure to check for what you've described with the insulation. That sounds very plausible indeed- especially with the rain!

Love the look of those older KWs!

Thanks again for taking the time,

Cheers!