General Question

z28proximo's avatar

Why does my truck start on its own, with no key, when battery leads are attached?

Asked by z28proximo (285points) July 11th, 2010

Initial specs: 2003 Ford Diesel F-250 Super Duty 7.0
2 batteries, 2 solenoids.

This all started out because it wouldn’t start, and had to be continually jumped off. Batteries checked out good, but a terminal was corroded through, so I replaced that. Batteries still wouldn’t hold a charge. Realized I didn’t reattach alternator lead to new battery terminal. Batteries charged now but next day it wouldn’t start again. Took off the starter and took it to autozone and they said it checked out, when I hooked it back up and connected the grounds to the batteries it started turning over the engine.

No key is in. Even with the key I get no power inside the cab even with the leads attached, except that the starter goes nuts trying to turn the engine over. It won’t start though, even when I try to jump it off and let the starter do its thing. Now one battery (the one closest to the starter) bubbles water when I connect the negative and gives a bad popgun or firecracker smell when it sparks.

Any ideas or hints? (Please excuse the long explanation, I’ve been wrestling with this for almost a week and left out quite a bit of the drama between me, the truck, and Autozone)

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9 Answers

dpworkin's avatar

Short in the ignition switch?

z28proximo's avatar

could that also cause it to not start at all, before I took the starter off? Before I removed the starter, it would just click when I turned the key.

LuckyGuy's avatar

Is the starter solenoid stuck in the engaged position? Whack it with a hammer. Seriously.

chyna's avatar

I’m not sure I would trust the folks at Autozone to help. I’d take it to a competent garage.
It could be anything, zombies, CIA, crop circles, etc causing this. Just saying..

cookieman's avatar

Is your vehicle named “Christine” by any chance?

z28proximo's avatar

@cprevite It’s funny you mention that, since it actually is my recent ex’s name…

The starter had a spacer on a connector missing that was shorting it out, replaced that. I went ahead and replaced the batteries with a marine battery and a spare battery for the RV and it cranked right up. As long as it works from here on out, then all of this trouble spawned from a simple bad battery terminal. But with fiddling with everything and messing things up that were fine while checking them out it got complicated. It all seems to be good now, though.

z28proximo's avatar

Spoke to soon, it won’t cut off without unhooking the batteries. Probably in the ignition. I’ll take it to a shop when I can.

aniisback's avatar

Check out the ignition part. It may be short or so.

Jabe73's avatar

If you want to do this yourself I would buy a cheap multimeter from autozone or any other stores (most places like Wal-Mart sell them cheap). Set the meter on dc voltage, test the coil terminals (on the starter solenoid) for voltage to make sure they are not energized when the battery leads are connected. If you are not getting voltage across your coil terminal to ground (around 12 volts dc) than you probally have a sticking/defective starter contactor. Another way to check this would be to disconnect the wires from the starter solenoids coil terminal (positive) usually and if the starter is still turning than you definitely know its the solenoid. If not than you have a more complicated problem within the ignition circuit itself and you may have to take your truck to a qualified mechanic.

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