Electrical problem

[azandy]

I have a 1950 Ford car V8 converted to 12 volt neg ground with a Pertronix distributor conversion and a one wire alternator.
The car does not shut off unless I disconnect the alternator. The three terminal ignition switch (I, B, Acc) is good and the alternator tests good.
Could the alternator still be at fault even though it passes the three test conditions at the parts store?
Thanks for any advice you may offer.
Andy

[Henry/Kokomo]

Did the car ever work correctly with the current wiring set up? On my alternator equipped 46 Tudor, there is a wire which is activated by the ignition switch that provides excitation current to the alternator. There is a diode in that wire to prevent the alternator from back-feeding through the wire into the coil. If that diode were not there or if it were shorted out, the net result would be that the alternator would feed the coil, even with the switch off. That would keep the engine running with the ignition switch shut off. Perhaps you have that problem. FWIW

[51 MERC-CT]

Doubt that the alt. has anything to do with it.
There is only one wire that goes from the ign. switch to the ballast/coil.
With the ign. switch turned off, see if the hot wire to the ballast/coil is live.

[1937pickup]

Did you just convert to 12 volt and put an alternator on the car? If so it is the alternator. I bet you have a place for two wires coming out of the back of the alternator, in addition to the large red wire . Ron Frances wiring sells a connector and wire that will take care of your problem. Once you "excited" the alternator by starting the car you need a way to break the connection to your ignition. Having said that you would be better running it as a three wire. Go to MAD Electric to read about the advantages of three wire.

[bbrocksr]

Originally Posted by azandy

I have a 1950 Ford car V8 converted to 12 volt neg ground with a Pertronix distributor conversion and a one wire alternator.
The car does not shut off unless I disconnect the alternator. The three terminal ignition switch (I, B, Acc) is good and the alternator tests good.
Could the alternator still be at fault even though it passes the three test conditions at the parts store?
Thanks for any advice you may offer.
Andy

Henry's got it right.
Bill

[31chevy]

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Originally Posted by Henry/Kokomo

Did the car ever work correctly with the current wiring set up? On my alternator equipped 46 Tudor, there is a wire which is activated by the ignition switch that provides excitation current to the alternator. There is a diode in that wire to prevent the alternator from back-feeding through the wire into the coil. If that diode were not there or if it were shorted out, the net result would be that the alternator would feed the coil, even with the switch off. That would keep the engine running with the ignition switch shut off. Perhaps you have that problem. FWIW

Ditto, Henry has it right I have 2 cars with that setup.

[31chevy]

You can buy a DA plug or you can get a diode at Radio Shack & make your own. google in da plug & it will explain it & give you options. Hope this helps.
Gary.

[39portlander]

Originally Posted by Henry/Kokomo

There is a diode in that wire to prevent the alternator from back-feeding through the wire into the coil. If that diode were not there or if it were shorted out, the net result would be that the alternator would feed the coil, even with the switch off. That would keep the engine running with the ignition switch shut off. Perhaps you have that problem. FWIW

When I took automotive many moons ago, this was a troubleshooting example that one of the "one way" instructors had rigged up for us to diagnose. Learning about diodes was fun. Scott

[34PKUP]

If 'azandy' has as he says a one wire alternator, isn't all this talk about extra wires meaningless?
My one one wire alt. has just one wire which runs from the alt. thru the ammeter to the battery side of the solenoid.

[George/Maine]

Do you disconnect when running the batt wire.
Your key switch could be bad,hot wire to coil from selinode,old wiring from 4 wire regulator.Pull the Pos coil wire see what happens,should stop.

[bbrocksr]

Originally Posted by 34PKUP

If 'azandy' has as he says a one wire alternator, isn't all this talk about extra wires meaningless?
My one one wire alt. has just one wire which runs from the alt. thru the ammeter to the battery side of the solenoid.

Probably not meaningless if he learns how to wire it correctly so the alternator doesn't power the coil when the switch is off.
Bill