My bronco ii started on its own

[Rabbos]

1988 ford bronco ii eddie Bauer 4x4 2.9 cologne
So i just left autozone for a part for my van, and i tried to start my bronco, but the battery seemed dead, so i pull out my battery jumper, and it comes on, but its making a horrible noise, so i turn off the ignition and take out the keys, and it stays on, still making the horrible noise. It eventually turn off, but like 5 minutes later while I’m inspecting the engine bay, it try’s to turn on again, keys out of the ignition, shuts off. I’m super confused about it, i got it on and working again as soon as my buddy shows up, no issue, so i drive down the street, hit a bump and it starts making a noise as if the starter is stuck, i park and pull out the key, and it STILL is running making this god awful sound, till i hear a hard thunk and it shuts off. Then i get nothing, but power, no turn over, I buy a new battery(which i needed anyway)checked all the fuses, still nothing. Thinking my starter just broke, i jumper the starter solenoid, and the engine starts to turn over, change that out, doesnt start till i battery jump it. Why and how do i prevent it from starting on its own, these past couple weeks its been struggling to start, as if the battery is drained when it used to fire up right away

 

[RonD]

Yes, the starter motor was running while engine was running, that's the noise, so plan on a new starter regardless

And replace the starter relay on the inner fender, called starter solenoid by some

You were saying it didn't "shut off" with key off and out, if starter relay was stuck closed then engine would just keep on spinning from start motor being on, its not "running" just spinning
With key off there is no spark or fuel injectors, and dash lights would all be off
If dash lights stayed on then your ignition switch, under steering column, may be bad as well

 

[rusty ol ranger]

Ive seen them do that with a bad battery before.

Its kinda freaky.

Check the little "S" wire on the solenoid. Make sure its clean, tight, and has juice

 

[RobbieD]

And do take a close look at your ignition switch (the electrical part).

 

[Shran]

Had a similar issue on my old 85 F250. It would just try to start itself at random with the ignition off. I had to leave it parked in neutral all the time, very annoying. It was a bad starter solenoid and it took a couple tries to get a good one at the parts store - several of them were bad in the box.

 

[Rabbos]

Got out yeah i was able to make it home after changing the solenoid, and it started up this morning right away, thank y’all!