Ignition switch won't shut down the motor

[Terry Carson]

I just replaced the alternator on my 1974 vintage Atomic 4, and coincidently the engine will not shut down with the ignitiion switch. I checked the switch, and replaced it, but the problem still exists. The alternator rebuilder also replaced the regulator with a unit that has an oriange and a purple wire and told me to connect the orange wire of the regulator which I believe is connected to the coil. Is there any connection at the alternator/ regulator that could be creating a bypass to the ignition? Could there be a problem with the replaced regulator?

[JimG]

I'm sure you'll get a more authoritative answer from someone that recognizes your wire colors, but connecting the regulator to the ignition coil doesn't make any sense to me. Maybe when he said "connect it to the coil" he meant the coil of the alternator?

Seems like an external regulator would only need to connect to the alternator output (as an input to the regulator), a wire to the alternator field coil (the output from the regulator), and ground.

If you confused the two "coils", the alternator wouldn't produce full output (without a field coil stimulus) but the regulator would probably drive the coil hard enough to maintain an ignition spark.

[Don Moyer]

The answer to both your questions is a qualified "yes". I would take the alternator back to the rebuilding shop and ask them to clarify the wire you are connecting to your coil. This wire should be the field exiting wire, and it should be protected with a one-way electrical diode to prevent it from feeding power from the alternator to your coil. It appears from your report that the wire has no diode and it's feeding power to the positive terminal of your coil, which of course keeps your engine running.

Don

[Terry Carson]

Problem Solved- But amp meter shows discharge

Many thanks Don. You were correct. The shop made the repair and the iginition switch shuts off the engine. One further question. The instrument panel amp meter shows a slight discharge reading after the initial startup. Reving the engine does not change the meter reading. I am assuming the amp meter measures current directly, and I would like to know what reading an independent amp meter would show if the amp meter is in the middle (neither charging or discharging) assuming there were no other electrical loads in use. I performed a battery load test and the battery appears ok.

[Don Moyer]

Terry,

It appears your alternator may not be functioning normally.

I'd confirm your alternator performance by measuring the voltage in your DC system. If your voltage is only 12 volts or so with the engine running, the alternator is not producing. If you have an original Motorola 35 amp alternator, your DC voltage should indicate approximately 13.5 volts with the engine running. Most modern alternators maintain 14.2 volts in the DC system.

Don