[goatman64]

I've been running an original Ignitor ignition for the past 18 years...engine is a 68 400 and, up until the install has run very well.
Wiring is all the stock harness.
Problem arises now that the car continues to run as normal when the ignition is turned off...power remains at the switch terminal where the Digital HP power feed is linked into.
The engine will stop by unplugging the 2 wire connector at the alternator with the key in the off position.
I presume this is alternator feedback from somewhere but can't track it down. I've read about instances where this happens in aftermarket ignitions and is cured by the use of a diode inline with the exciter wire...
The car otherwise runs fantastic and lights instantly with the box connected.
Can anyone speak to this issue?
Thanks so much!

[Geoff]

You need a diode. How to connect it is shown on the MSD website.

[Kenth]

Sounds like you are using a power source to the coil not controlled by the ignition switch.
AFAIK 1964 GTO uses one #1 IGN and one #2 IGN wires to the + terminal on coil.
Use both these wires to the #86 terminal on a regular 30 amp single relay. #85 on relay to ground, #30 to battery and #87 to + on coil.
This way you´ll have an ignition switch controlled full power source for your aftermarket electronic ignition system.

HTH

[george kujanski]

The ignition you are using most likely uses a sense wire from the ignition circuit to trigger an internal relay/switch to grab running power from the battery, or are using a relay triggered by said wire.

The problem is that the idiot lite connection to the alt backfeeds enuf current to keep the trigger circuit alive. A diode in that circuit eliminates the backfeed.

In a standard ignition connection, the ignition coil circuit current requirement is much larger than the backfeed current so the ignition dies.

George

[goatman64]

Great! Thanks for the help everyone.
I'll see what kind of options I have locally.