Engine won't turn off, WTF

[antonm]

So, I recently picked up my 74 Bronco that the PO said didn't run. Well, I got it to run, but when I turn the key off (and remove the key from the ignition) the motor just keeps right on running. I pull the power lead off the coil to shut it down. While I'm planning on converting it to EFI and doing a full wiring harness anyway, I'm still kinda curious as to what this could be. Is this a common occurrence? Its a factory 302 /C4 right now.

 

[farzadmip]

It happened to me, it was the solonoid in my case but I believe it could be a number of things. Be sure to disconnect at the battery until you get it figured out.

 

[half cab]

Solenoid switches (starter relay) for the most part are made in China now. I went through three before finally finding a USA made one at NAPA but that was just by chance they found an older o.one on the shelf .

Also could be the ign. switch but most likely the solenoid.

 

[wegngis]

A long time ago in another vehicle (1975 AMC) I had the same thing happening. Turns out a bad alternator was causing it. Once I swapped it out, it completely went away. Didn't make a lot of sense to me, and I've had people tell me I'm crazy since, but results don't lie. Right? %)

 

[half cab]

A long time ago in another vehicle (1975 AMC) I had the same thing happening. Turns out a bad alternator was causing it. Once I swapped it out, it completely went away. Didn't make a lot of sense to me, and I've had people tell me I'm crazy since, but results don't lie. Right? %)

I know and I've had weirder things happen pertaining to the dimmer switch then I care to rehash .;D

 

[wegngis]

Just because I can't resist, let me tell you about the weirdest one for me. I was driving my Ford Escort home one day, and every time I hit the brakes the car would try to stall. Turns out my negative terminal was pretty darn loose. I think the extra draw created by illuminating all those lights was enough to send the system into a tizzy. Tightened it up, and all was well.

We now return you to your normally scheduled thread....

 

[DirtDonk]

Yep, lots of funny things go on under a hood or dash on these old rigs. Some new ones too!
Generally though, the two things most common to do that on an EB were already mentioned as the ignition switch failing, and the starter relay failing. What happens at the starter relay is that the Brown wire on the "I" post that normally gets powered up only during START, is shorted out to battery power somehow (should be pretty fail-safe, but they're not apparently) and feeds power directly to the ignition coil even though you've turned off the key. It's a bypass, so independent of the ignition switch.

Otherwise, as you said this is a PO nightmare (for him at least) and they might have even tried messing with stuff. YOu might have a bad wire, connector, short or other mishap somewhere that's contributing to this.

Paul

 

[DirtDonk]

Oh, but congrats on getting it running at least!!!;D

Paul

 

[Broncobowsher]

The ignition circuit is modestly basic. There is very little tied into the ignition itself (not related to the accessory side). At this point you are having issues with power not being cut off. Should be fairly easy to trace down.

The ignition switch power the ignition and charging circuits. Turn the key to run and they are both powered up.
There is a bypass from the solenoid to the ignition to give a little extra electrical boost while the starter is engaged.

The easiest to check is a bad solenoid. With the engine running and the key turned off, pull the "I" wire off the solenoid. If the engine still runs, that isn't the problem.

Next is the voltage regulator. These do go bad, the have both battery and ignition power present in them. They can backfeed the ignition system. I don't recommend unplugging while the engine is running as it can hurt the regulator if it isn't already bad. But you can run the engine with it unplugged and see if it turns off normally. If so you have a bad regulator.

Last is the ignition switch itself. A bit more bastard to deal with because it requires fighting under the dash no matter what. If going through the trouble to pull it out and check, might as well just put a new one in for all the effort.

And there is always the possibility that the previous owner did some funky wiring job that we can never diagnose.

 

[antonm]

Thanks all. I'll probably swap out the solenoid and see what happens, I'm sure I've got another ford starter solenoid laying around. Just thought it was funny that I finally got an early bronco and it turns out to be possessed

 

[jwhit]

The ignition circuit is modestly basic. There is very little tied into the ignition itself (not related to the accessory side). At this point you are having issues with power not being cut off. Should be fairly easy to trace down.

The ignition switch power the ignition and charging circuits. Turn the key to run and they are both powered up.
There is a bypass from the solenoid to the ignition to give a little extra electrical boost while the starter is engaged.

The easiest to check is a bad solenoid. With the engine running and the key turned off, pull the "I" wire off the solenoid. If the engine still runs, that isn't the problem.

Next is the voltage regulator. These do go bad, the have both battery and ignition power present in them. They can backfeed the ignition system. I don't recommend unplugging while the engine is running as it can hurt the regulator if it isn't already bad. But you can run the engine with it unplugged and see if it turns off normally. If so you have a bad regulator.

Last is the ignition switch itself. A bit more bastard to deal with because it requires fighting under the dash no matter what. If going through the trouble to pull it out and check, might as well just put a new one in for all the effort.

And there is always the possibility that the previous owner did some funky wiring job that we can never diagnose.

i have seen guys hook up voltage regulator wrong and this can happen
make sure green wire at regulator is on correct post if not it will keep power going to coil when switch is off

 

[DirtDonk]

Thanks all. I'll probably swap out the solenoid and see what happens, I'm sure I've got another ford starter solenoid laying around.

If you have another one already, then nothing wrong with testing by swapping. But it's easier still to just disconnect the Brown wire and try again.

Just thought it was funny that I finally got an early bronco and it turns out to be possessed

That's actually the norm, rather than the exception.

Paul