engine won't stop cranking

The starter solenoid stuck. When you have low voltage/slow cranking, the starter pulls a lot of amperage, which probably fused the solenoid contacts together. You have to test things out to be sure which one is giving you trouble, you have the solenoid on the starter (often called the bendix), plus another one should be mounted right by it. The truck itself may have one too on the firewall.

The second one mounted on the starter is very important for a 39MT, but many people leave them off. Leaving it off usually works for a while, but eventually it overloads the crank circuit in the truck. That solenoid is there because the 39MT bendix solenoid draws more current than a 41MT. It is there to protect the truck wiring.

 

Sometimes you can tap the starter solinoid with a hammer and it will stop turning.Good luck.

 

that was my suggestion. hit the starter just to jault it a little, so maybe it'll wake up and set it self properly.

 

Do yourself a favor put in a new starter 99% of the time it's the starter better keep that 9/16 wrench in your pocket I'm also a firm beliver in battery disconnect switches lots of trucks have burned to the ground because a failed starter

 

It depends on the solenoid in the firewall and the OEM wire gauges. Most trucks are built for a 41MT starter. The 39MT solenoid draws more power. If the vehicle wiring can take the extra current, it's OK. Most are not built to handle the extra current and it eventually kills the OEM solenoid or wiring, which sounds like what happened to you. For the most part, they work fine, but slow cranking in cold weather and/or low batteries puts an extra current draw on it.

Without the extra solenoid, it's a gamble. Having it never hurts, even if you don't need it.

 

I've never heard a truck burning down because of a bad starter. Could you explain more? I'm not being smart if it sounds like it, I really would like to know. This is a first.

 

And I'd like to know more about adding battery shut off posts.... That sounds like a great idea.. Does anyone sell a kit ? or is it a dealer thing ?

 

I've seen two things happen one the bendix sticks when you hit the key or the selinoid and it keeps cranking until the battery's are disconnected or the battery cables overheat and superheat melting the insulation and resulting in a fire I have also. Personally seen trucks starters fail and start cranking after sitting in the yard hours after parked i suggest running a hi torque starter instead of the older 39mt or 42mt also I suggest running a battery disconnect in case of emergency.they will not hold up that great on the positive side of the battery.i put them in the negative side of the cable you can run a small jumper wire with a 2 amp fuse to keep your ecm voltage and clocks and radio look at flaming riverthey are one of the best I have run