TO20 ignition switch will not shut off engine

[Dave Kay]

First, I would like to address the terms One Wire and Three Wire alternators. Technically speaking, the one wire self-exciting alternator is actually a two-wire alternator.
Whether you use a #10 AWG wire from the ground terminal of the alternator to chassis ground or have the alternator case ground through the mount, it is two wires. In the case of
the three-wire alternator. The battery terminal goes to an ammeter to the starter switch to the battery; a jumper goes from the battery terminal to terminal 2 in the alternator;
terminal 1 goes to the Charge Indicator Lamp and last but not least, the ground wire to chassis or case ground through the mounting. This is 4 wires.

It should be noted, terminal 1 carries full system voltage. In the 4-wire system, the ignition switch and coil are on two separate lines. This is why the engine keeps running with
the ignition switch off, when you don't have a diode between terminal 1 and the Charge Indicator Lamp. By the way. without the diode and engine off, your battery is being drained
and your ignition system destroyed.

 

[wore out]

''By the way. without the diode and engine off, your battery is being drained and your ignition system destroyed.''

That is simply NOT true.

While certainly I agree that a diode, ''idiot light'' or resistor IS needed to eliminate or reduce ''backfeeding'' to the ignition circuit preventing the engine from shutting down once the engine is stopped the presence or absence of a diode in the ''excite'' circuit has NO effect on battery drain or ''destruction'' of the ignition system.

 

[JMOR]

(quoted from post at 11:34:40 04/14/23)
''By the way. without the diode and engine off, your battery is being drained and your ignition system destroyed.''

That is simply NOT true.

While certainly I agree that a diode, ''idiot light'' or resistor IS needed to eliminate or reduce ''backfeeding'' to the ignition circuit preventing the engine from shutting down once the engine is stopped the presence or absence of a diode in the ''excite'' circuit has NO effect on battery drain or ''destruction'' of the ignition system.

ot to mention that he doesn't know that an UN-insulated cast iron engine block, brackets, aluminum alt case are NOT "wires"! A current path, they are, however.

 

[rvirgil_KS]

1. It should be noted, terminal 1 carries full system voltage - - yes, (assuming terminal 1 on alternator) full system voltage but not full system current.

2. the ignition switch and coil are on two separate lines. - - Not true. The coil and switch are in series on the same line.

Coming out of the ignition switch a connection goes to the coil and a parallel connection to the #1 excite pin on the alternator. At start up voltage from the switch excites the alternator to start it to charge, then output from diode trio in Delco alternator supplies operating power to the internal regulator. When you turn off the switch, battery connection is disconnected from the coil but power from the diode trio through #1 pin feeds back to the coil and allows engine to keep running. Either a diode to block reverse current or a lamp or resistor to limit current below level needed to operate ignition system are inserted in the wire from switch to #1 pin to block feed back and prevent engine run on.

3. when you don't have a diode between terminal 1 and the Charge Indicator Lamp - - you dont need a diode when you have charge indicator lamp. Either one, but not both.

4. without the diode and engine off, your battery is being drained and your ignition system destroyed.
- - With switch off and engine not running there should be no power available at pin #1 or the coil. Reverse biased diodes in the alternator prevent the battery connection to back of alternator from discharging the battery.

5. In a discussion of 1 wire vs 3 wire alternators the active connections are counted and ground is assumed.

 

[Dave Kay]

I stand corrected. I did not know the charge indicator lamp had enough resistance or that the diode trio prevents back feed. Even though I was incorrect, I would like to explain why I said the ignition switch and charge indicator lamp are on separate lines. It was my belief that in the absence of a diode, power would continue to be applied to the ignition coil even with the ignition switch in the off position thereby, creating an alternate route for the ignition and thus, two separate lines.

The reason I addressed the issue of one wire and three wire was due to a conversation I had with an alternator manufacturer. When asking a question regarding the one wire
self-exciting alternator, he became obviously agitated at that description and went into a diatribe as to why the ground should be considered a wire.

 

[sunbeam]

The exciter wire will feed back the ignition without resistance but when the alternator is not turning there is no voltage to feed back. Even just a momentary push button switch will work once excited it will charge until the alternator quits spinning.

 

[Mad Farmer]

Maybe get the multimeter out and trace voltage back from the coil, or the switch, when it won't shut off.

Could it be the switch?