[azbirds]

I'll check tomorrow.

[azbirds]

It's been a while, but finally had a chance to do some more. I put a new ignition switch in, and that didn't help. Pulled the bulb out of the Gen socket, that didn't help. At least I don't feel so bad about not finding this problem, I thought it might be something obvious that I was just missing. Could it be melted wires inside the harness? It is a nearly 50 year old piece.

["QUICK-SILVER"]

Unplug the instrument cluster and see what happens.

Depending on what happens, it'll help narrow down where the field wire power is getting into IGN-1 circuit.

If it cuts off, there's a short in the printed circuit or in the harness between the printed circuit and ignition switch.

If it continues to run, there's a short in the harness somewhere inbetween the cluster plugin/connector and the alternator plugin/connector.

Just more to try
Clay

[Blued and Painted]

"azbirds Could it be melted wires inside the harness? It is a nearly 50 year old piece".

Have we checked the fuse links shorted to R terminal down on the starter?

[Simple Man]

Years ago, I changed the battery ground cable on a 66 Ford Mustang. The car would then start, but would not shut off with the new cable. Is it possible you have a ground problem between the body, and the battery?

[GT182]

I'd say it's the ignition switch. Turning the key off doesn't break the connection for voltage to run the engine.

But do check the ground wires for the engine to the frame. Tho they shouldn't matter as much as the ignition switch does. it doesn't seem possible the 2 or 3 ground cables would all be broken.

[azbirds]

Thanks for all the replies. More stuff to check. Wiring at the starter looks great. I will check all ground straps, and even put in a temporary one to supplement. the main harness into the instrument cluster is a massive PITA to get loose, but I will try that also. I'll try to get it done by the weeks end, and post my findings.

[smasse64]

...i would say ig switch, as was my 64 lemans...but also check volt reg ground, but you are internal..so maybe other ground issues..not broken, but dirty...sometimes just cleaning and tightening various grounds are all you need.

[azbirds]

Still not solved. I had to put it on hold, and use it as is. Life gets pretty crazy sometimes. No fuseable links. Replaced the ign switch. I'll try the addition of some temporary ground straps next.

[rohrt]

http://www.mwbauto.com/images/Full/6...-Rear-Half.gif
http://www.mwbauto.com/images/Full/6...Front-Half.gif

I would work backwards from the coil if possible. You must be getting some bleeding voltage to the purple wire on the coil. Using the drawing above I see the purple goes back to the bulkhead connector and then splits to a Yellow and Blk-Pink. They both go back to the ignition.

I would draw out the connections of the ignition by hand. I can't find a drawing.

*Red + incoming hot wire
*purple that runs from the starter solenoid through the neutral safety switch. (This would be the one that gives you full 12volts while cranking only. Check this one first)
*Pink - looks like it feeds the flasher and back up lights
*Brown - Looks to feed wiper motor and downshift solinoid.
*Brown/wht - going to alternator

[Joe's Garage]

You mentioned that the engine died when you unplugged the alternator with the ignition key OFF. Right?

I've had to use the diode in dozens of MSD installs, both with the internal and the external voltage regulators.

EVERY SINGLE ONE that RAN ON when the key was off STOPPED DOING THAT with the diode installed.

Here's a second charging circuit check procedure to try: With the engine OFF, unplug the alternator. Now start the engine. It won't be charging, but who cares, it's only for thirty seconds or so. Turn the key OFF. Does the engine stop running?

I'd be willing to bet it does.

The fact that your engine stopped running when you unplugged the alternator the first time indicates that some issue in the alternator circuit is feeding back voltage.

And if the alternator is charging the battery correctly, and the battery holds that charge, it can't be too big of an issue, can it?

After this new test, if the key works to turn the engine off with the alternator UNplugged, that confirms, once again, that the ignition circuit (so far as the switch and key are involved) functions correctly.

And it also confirms that the stray voltage is coming from the alternator circuit.

Rather than needing to figure out precisely WHY this condition suddenly appeared, I would just install a 1A-100V diode from Radio Shack somewhere in that wire from the alternator to the GEN light. Hide it somewhere in the harness and wrap or tape it back up. No-one will ever know it's there but you.

And your KEY will work again.

Problem solved.

Drive and enjoy.

Here's a link to MSD's diode install instructions:
https://www.msdperformance.com/suppo...s/#EngineRunOn

Here's a quick test to see if an additional ground strap would help: Clamp one side of a set of jumper cables on the negative terminal of your battery and the other end of that side to the alternator case. I use the lug where the bolt is that you use to tighten the belt.

With the jumper cable in place, does the key turn the car engine off? If it does, it could be a ground issue.

Or just install that diode and get on with life.

[azbirds]

Well, Joe. You hit the nail on the head. Alt unplugged the engine shuts off with the key. I will be installing a diode so I don't have to look farther into it. When I restore the car again that will be a good time to check the harnesses closely.

["QUICK-SILVER"]

With the GEN bulb out the circuit between the alternator and ignition switch "should" be open.

Diode may get the car where you can cut it off.

But, still don't know where or how power from the alternator is getting to the coil.

I suspect a short in the printed circuit since the GEN light doesn't work. But could be anywhere in the brown wire from the switch out to the alternator.

Please keep us updated if you ever find the real problem.

Clay

[azbirds]

I definitely will.

[Geoff]

There is usually a resistance wire [ not to be confused the OTHER resistance wire that goes to the ign coil ] wired in parallel in the wiring loom across the gen light so that if the light fails, the alt still charges. So if your alt is still charging/engine continues running in the off position with the gen light out, this is how it happens. Diode will fix it.

[george kujanski]

Usually this situation occurs if a relay is used to control power to the dist/coil, HEI, or MSD box. There is enuf current thrut he idiot lite circuit to keep the relay on providing power to the ignition circuit. The diode prevents this feedback. With a std ignition connection (without the mentioned relay, etc. the idiot lite leakage cannot support the current requirements of the ignition and the engine dies.

If no relays etc. are used, the only way the ignition can run is a good connection to the battery, i.e. faulty wiring, bad ign switch, etc.

George