Engine won't shut off

[gsjohnson]

I have installed an MSD on my 68 2.0, along with their 8910 Tach adapter. Everything was operating as it should for several weeks and then my Tach started fluctuating and not holding a study read. I did the usual things, checking the point gap to see if it had slipped and rechecked the timing. Everything was where it should be. It was suggested to me that tension setup in the tach may have gone bad. I called North Hollywood Speedometer and spoke with Kevin who suggested that I have the Tach converted to eliminate the Tach Adapter while he was in there. I did as he suggested and the tach came back the same week looking brand new. I removed the MSD Tach Adapter and installed the tach. Started the engine and the tach worked as he stated it would without the tach adapter. I then take the car down to the local gas station to fill it up and the engine won't shut off when I turn the key to the off position. Then suddenly the engine turns off...I discovered that with the key in the off position, the engine will only shut off when I apply the brakes. I'm assuming the brake lights are somehow triggering the ignition to shut the engine down. Any theories out there that might explain what's happening?

[304065]

Where is the tach connected? It should be connected to the tachometer output on the MSD (you don't say which one, so I assume a 6AL, which has a 1/4" male faston on the end. Connect the tach to there.

Next: What is your wiring diagram for this installation? It should be this:

Fat red-- B+ (tap off the terminal block on the electrical console, do not break the central fin on the bakelite connector)
Fat black- ground- wire to ground lug forward of electrical console
White- points
Small red- ignition- this is a red wire in the harness that goes to a "wye" to power the hardi fuel pump on one branch and the coil on the other. Since you aren't using kettering ignition anymore, you tap into this for the switched +12v from the ignition.
black, yellow coil wires

That is it. Let's start with that and work from there. Be careful with electricity it can kill you or burn the car down.

[porschestrabe]

I did a restoration on an 83 911sc cab and had the same/similar problem ( I found that the fan slider switch if left in the on position would keep the car running, turn the fan off the car would turn off with key in the off position) If I recall the alternator light in the tach plays an important part in turning off the car. Try disconnecting the light be careful with the dangling lead and see if the car will stop and start. Wish I could be more help. I may have also installed a resistor or diode in line? I think it is caused by stray positive power back to the ignition system and bypassing the ignition switch.

[sithot]

Be careful with electricity it can kill you or burn the car down.

It's like they say, "All good things must one day be burnt to the ground for the insurance money." Mickey Cohen (Sean Penn)- Gangster Squad.

On point I just saw this very problem in a car. The ignition (12v) wasn't switched through the battery. Turn the key off and she kept on running.

Tom

[304065]

It's like they say, "All good things must one day be burnt to the ground for the insurance money." Mickey Cohen (Sean Penn)- Gangster Squad.

Where do you GET this material? I am incorporating that into my personal lexicon.

Back on topic-- yes, making sure the small red is wired to switched +12v is key to a correct install. And you get better gas mileage if you can shut off the car!

[gsjohnson]

I will look into these suggestions over the weekend and report my findings. Thanks to all for the suggestions.

[sithot]

I wasn't serious about collecting insurance money. Just want to clarify that in case...

Tom

[rothsport]

This I have seen a number of times. It is simple to fix. Buy a 1A-100v diode from Radio Shack. Pull out your instrument containing the alternator light. Install the diode in line on the blue wire close to connector at the bulb.
Diodes are directional and marked by a band. The band faces the alternator, not to bulb. The diode prevents alternator feedback to the MSD when the key is turned off.

[gsjohnson]

Where is the tach connected? It should be connected to the tachometer output on the MSD (you don't say which one, so I assume a 6AL, which has a 1/4" male faston on the end. Connect the tach to there.

Next: What is your wiring diagram for this installation? It should be this:

Fat red-- B+ (tap off the terminal block on the electrical console, do not break the central fin on the bakelite connector)
Fat black- ground- wire to ground lug forward of electrical console
White- points
Small red- ignition- this is a red wire in the harness that goes to a "wye" to power the hardi fuel pump on one branch and the coil on the other. Since you aren't using kettering ignition anymore, you tap into this for the switched +12v from the ignition.
black, yellow coil wires

That is it. Let's start with that and work from there. Be careful with electricity it can kill you or burn the car down.

Thanks John your suggestion resolved the issue. Although it worked properly, I had the tach wire attached directly to the points. When I moved the connection from the points to the MSD tach output it did indeed resolved the run-on issue. Interestingly enough, this problem never occurred until I had the tach converted to operate without the tach adapter.
For some reason I am thanking you again for your assistance

[gsjohnson]

Update: Initially after changing the tach wire attachment, I had shut the motor off 2 or 3 times in the garage and the run-on seemed to be corrected. But then I took the car out for 10 mile run and when I returned home, the engine again would not shut off. I will install the diode next, which I believe will resolve the issue.