Engine will not turn off
 

Recently fired the engine in my 68 fire bird and all was fine except the alternator was not charging. Sorted that out, the field wire on the alternator was open circuit. Alternator now charges and engine starts fine but will not turn off at the key in the off position. I am running a HEI and have installed a relay that is driven from the old coil wire and new heavier power leads through the relay to the HEI. Any Suggestions.

Thanks

do you have power to the coil all the time? something miss wired or bad ignition switch?
old coil wire is it hot key on/ dead key off? you got relay wired correctly?

Unplug the alt and see if it shuts off

You need to install a diode so that the 12 volts does not back feed and power the coil.HEI.

Is this an internally regulated 10SI or 12SI style alternator? There are two wires on the DA plug on those alternators. One is the voltage sense that gets connected to the B+ wire. The other is the regulator energize wire and it goes to a switched hot (but not the ignition circuit). The regulator energize wire outputs enough voltage once the regulator is working to keep the ignition system powered. This is why that wire is usually connected to an accy circuit that is switched ON by the key, but isolated from the ignition wire with key OFF.

If this is an older externally regulated alternator, a similar theory applies, but I don't know which wire you need to switch on/off.

The alt idiot lite circuit is backfeeding the ignition circuit as stated. This is common when using the relay to power the HEI. the backfeed has enuf current to keep the relay on. In a tradiitional connection, the coil itself would be in the connection and there is not enuf power supplied by the idiot lite circuit to keep the coil powered.

If you keep the relay, install a diode, (1N4001 thru 1N4007 available at Radio Shack) in series with the idiot lite brown wire, (terminal 1 on the alt plug), the band end of the diode towards the alt.

George

this happened on my 67 gto when i installed an msd ignition system on it.
turned off the key and pulled it out. ran just like i never shut it off.
installed a 1A 100V diode in the brown wire (#4 at the voltage regulator)
and the problem went away. like george k. said, the idiot light circuit is back-feeding into the ignition circuit. :2cents: