Here’s how I understand a starter to work

1) A signal tells the solenoid to activate

2) The solenoid, via the magic of magnets, pushes a shaft with a sprocket out

3) The sprocket mates with the ring gear on the flywheel

4) Something...(and this is where I’m a bit confused) tells the starter motor to spin

5) The starter motor, using raw power from the battery, spins the solenoid shaft, which turns the sprocket, which turns the flywheel, which starts the car

Regarding step 4, and basically my question...what tells the motor to spin? Namely, does the solenoid internally tell the starter motor to spin, or is there a separate signal that tells it to spin?

I’ve got some sort of electrical issue with my car in which, sometimes, when I try to start the car, it begins to start, but it seems that the solenoid retracts the sprocket and the motor begins spinning freely - due to a short of some sort, it keeps on spinning for some indeterminate amount of time. I jump out of the car, pop the hood, grab a wrench, and disconnect the battery cable. Sometimes, before I can even get that far, the motor stops spinning on its own and the car can typically be started as normal. This morning, the short persisted between several disconnect/reconnect cycles of the battery until the “issue resolved itself”. I’m trying to sort out which circuit has the short.

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Here was my debug process, basically.

1) Tried to start the car - engine turned over a couple times, but then stopped turning over - I could hear the starter motor still spinning freely (sounds a bit like a loud fan at that point, a steady smooth whirr). This is how the issue has always presented itself

2) Popped the hood and disconnected the negative on the battery - the motor stopped spinning.

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3) Touched the negative to the battery - the motor started spinning again, and I quickly removed it.

4) Disconnected the starter signal wire and repeated step 3, same result.

5) Disconnected the chassis power from the Starter/Alternator dedicated power, and attached only the starter power to the battery, and repeated step 3...

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6) ...I touched the negative to the battery - the motor spun just a bit and then stopped before I could remove the negative. I touched the negative again, and the motor was no longer spinning. I reattached the negative and the chassis power (reversed Step 5), started the car as normal, and drove away.

Now, step 6 is how this problem always resolves itself, sometimes before I can even do step 2. Unfortunately, that makes debugging harder - the reason I posted this today is that this is about the 6th time this has happened, but today it lasted longer which is good and bad. Bad in the sense that, well, it’s bad, but good in the sense that I was able to get this far debugging

Thanks