There was a couple of below zero days this week here in Co. After "wait to start " light went off I cranked the engine. When the engine started slowing down and I knew it wasn't going to fire, I turned it off.The engine kept cranking ! I pulled out the key...still cranking. I jumped out my 97 F250 and grabbed a wrench and disconnected one of the batteries. After about a minute I reconnected it and started cranking again. I pulled off the ground cable again and went into the house to get warm. After about a half hour I connected the battery back up,no cranking,I put the trickle charger on it. Next day I checked my block heater...It wasn't working. Troubleshooted it. Ohmmeter said the heating element was good, the cord was not. I repaired the cord, plug it in. After about two hours, the engine was warm, the batteries were up and it Fired ! My question, why did the engine keep cranking with the key off !

 

I just had a similar problem kinda it was the starter relay.

 

never heard of this but the only thing i could think of is an ignition problem, like it sticking on, or a starter problem not releasing the gear, and continuing to to supply power to it. Waljon might be onto something with the starter relay.

 

Batteries are too low on juice.
I've had it happen to me several times.
Charge the batteries, or repalce them.