There are probably others more familiar than me with this type of setup, however, here goes. I think usually the way of turning off a magneto is by switching a short across the points. There is of course no battery power going into a mag, so you can't turn that off. On the other hand, the light switch is usually arranged to switch battery power to a bulb. So there will be one connection to the battery live side, and as many output connections as it has functions, eg one for headlight, one for sidelight and so on. So the switch is intended to switch power to a load, while the magneto needs a connection made to ground for off.

So if the switch is being used to switch lights, it probably cannot directly be used to control the magneto as well, however it can be done indirectly. Suppose you want the "side" to turn the ignition on. You provide a relay with a suitable coil, 6V or 12 Volt depending on the battery. You connect a normally closed contact set across the magneto points. When the switch is in the on position, the relay pulls in, the contacts open, and the magneto operates as normal, When the switch is off, the relay drops out, the contacts close, and the sparks stop happening. If it is on a motorcycle, you want a good robust relay as vibration is not good for this sort of thing.

If the switch is not also being used to control anything else, you could also use just the switch on its own, however the "on " position would short the points, stopping things, and the "off" position would allow the engine to run. You wouldn't need a battery for that setup.

John

The standard "Off", "Side", "Head", switch merely connected the battery feed, to the side lamp circuit, and then to the Headlight circuit.

They came in three forms. In one the ignition switch was merely a knob that controlled the feed to the ignition

A more sophisticated version did the same thing, using a simple "spade" key. When worn the spade could fall out. leaving the engine running (I remember having to stop and retrieve my keys from the road, when they fell through the gap around the handbrake lever!)

The more secure version operated the ignition switch by a key switch. For many years the face of the switch carried the key code. Until clever thieves used a telescope to read the code, went and bought a key and unlocked the car to steal it without any need to "hot wire".

On vehicles fitted with a three brush dynamo,, in the OFF position it left two resistors in the feed to the third brush, minimising the charge rate to the battery.

The "Side" position shorted out on resistor, increasing the charge to compensate for the side and tail lights.

In the "Head" position the second resistor was shorted out, delivering maximum charge to compensate for the electrical load of the headlights.

To stop a magneto equipped engine, you have to short out the mag, as the piklots of rotary engined aircraft did during and after WW1.

Howard

As the mag is self contained you would have to draw wires from it internally, why would you want to do that?

I only have knowledge of some post war Lucas motorcycle magnetos.

The K series, used on twins, were rotating coil magnetos and usually had a kill switch. This shorted out the contact breaker and was located either on the end of the magneto or the handle bar.

The SR series, used on singles, tractors dumper truck engines etc, were rotating magnet magnetos. When fitted to motorcycles these did not have a conventional kill switch, the engine was stopped using the valve lifter. However the engine could be stopped by pushing the name plate on the magneto against the body (this is difficult on my bike since the plate is very close to the front of the barrel). Using the mounting screw for the plate I did once wire in a handle bar kill switch to do plug chops.

I doubt if I have answered the question.

JA

Aircraft engine magnetos are generally rotating magnet magnetos and these do have cockpit kill switches.

Edited By JA on 05/06/2021 12:18:17

My RE Constellation, and Intercepter both had Lucas mags with the kill button wire connection in the centre of the end cap. I just used a press to make button on the handlebars. Not all mags had the stop facility, it might have been an extra.

Over the pond, Lucas was referred to as "the prince of darkness", although the worst electrical system I had on a motorcycle was on a PUCH 125 by BOSCH.

Edited By old mart on 05/06/2021 17:56:36