Ignition switch problem

tho coolin fans generate enough power to keep the engine running fof a short time. I think there are diodes that stop the power from backfeeding the ignition system, or you can isolate them with relays.

quote:

Originally posted by 72GTS:
tho coolin fans generate enough power to keep the engine running fof a short time. I think there are diodes that stop the power from backfeeding the ignition system, or you can isolate them with relays.

Mine sometimes continues to run because of the fans as well. Try stepping on the brake pedal when you turn it off. On my car the brake lights draw enough power for it to stop normally.

Thanks.
But it's not the fans drawing power as they switch on & off at 80 degrees C.
Often I cannot shut the engine down when it's only been running on cold start up with no fans on.

regards,
Tony.

If you are running an MSD and a standard ford voltage regulator you may need to add a diode.

I came across this when I recently installed my MSD 6AL, it's from the instructions manual:

ENGINE RUN-ON
If your engine continues to run even when the ignition is turned Off you are experiencing engine Run-On. This usually only occurs on older vehicles with an external voltage regulator. Because the MSD receives power directly from the battery, it does not require much current to keep the unit energized. If you are experiencing run-on, it is due to a small amount of voltage going through the charging lamp indicator and feeding the small Red wire even if the key is6turned off.

Early Ford and GM: To solve the Run-On problem, a Diode is supplied with the MSD in the parts bag. By installing this Diode in-line of the wire that goes to the Charging indicator, the voltage is kept from entering the MSD. Figure 6 shows the proper installation for early Ford and GM vehicles.

Note: Diodes are used to allow voltage to flow only one way. Make sure the Diode is installed facing the proper direction (as shown in Figure 6).

Ford: Install the Diode in-line to the wire going to the “1” terminal.
GM: Install the Diode in-line to the wire going to terminal #4.
GM: 1973 - 1983 with Delcotron Alternators.
GM: Delcotron Alternators use an internal voltage regulator. Install the Diode in-line on the smallest wire exiting the alternator (Figure 7). It is usually a Brown wire.

MSD 6AL

Kristian

You guys nailed it,(1973 Pantera).
I just went out into the workshop & fired the beast up again.
Turned off the ignition........nothing, hit the brake pedal & it shut down.
Tried it a few times & the pedal works every time.
Its only been doing this since I installed the injection & Motec.
Previously when it shut down I must have had my foot on the brake & not realised it.

Pulling the ignition switch apart was not a job I was looking forward to, I just presumed it was on its way out with age.

So now I'm just waiting for the front & rear hoods to come back from painting.

Thanks again.
regards,
Tony.

Glad we could help.

Push1267 has an excellent point about the MSD ignition. I actually think that my MSD6A is the primary culprit for my run-on. It doesn't take much voltage to keep the fire lit with it, but the brake trick works every time.