Boyer Powerbox question

You cannot use the ignition switch as a Mag kill switch. They work the 'wrong way'. I do do a Magneto ignition switch, but it needs a 19mm hole. The light is up to you. I also do a charge warning light device that could control a lamp. see AOSERVICES.CO.UK

... by powering a N/C or changeover (with 87 and 87a terminals) relay such that when the ignition is switched on the contacts are open and when off they will close. Then use the switched contacts to earth the mag cutout when powered off.

Do you have the original headlight shell? Whichever ignition system they had, there was the switch on the left and ammeter on the right.  Why not keep what you have, but without using the ignition circuits?

Allan - relays are quite simple devices that use a "trigger" voltage to switch another voltage. They can be arranged to that when a voltage is applied the secondary circuit is closed, or, for your purposes, opened. You need a changeover type relay. This site has a good explanation: https://www.12voltplanet.co.uk/relay-guide.html

The  terminals on the common relays available from accessory shops etc are marked as follows:

85 and 86 for the trigger (one to your ignition switch, the other to earth), 30 to the kill switch connector on the magneto, and 87a (only present on changeover type relays) to earth. So when you switch the ignition on the relay will open thus allowing the magneto to spark. When switched off the relay will close thus earthing the mag and stopping sparking.

that sounds right. As with all electrics it's as well to check carefully with a multimeter that everything works as intended.

Yes you could put a kill button either piggybacking on terminal 30 or direct from the mag contact - obviously earthing through the bars although with grease in the steering head bearings this isn't always perfect. I usually have a dedicated earth wire from under something like the air lever clamp so that I know the horn etc will work.

I find relays are a simple solution to many problems which are often overcomplicated by people. For instance I had an indicator warning buzzer on one of my modern bikes that used a relay triggerd by the stop lamp feed to silence it when I had the brakes on such as at traffic lights.

There is a subtle problem here quite a few people thank that owning a mutimeter allows them to understand its usage and often believe what it tells them, when in fact things are NOT. Some basic instruction from books and some one who knows about these things and can teach is what you need. Owning a multimeter is NOT any answer.

The key is rather large but I fitted a stainless bracket, forward of the top fork centre nut.

I can send a photo if you wish.

BTW, thanks to much help from Jon and John, I wonder where I can buy a suitable relay to help my electronic tacho work properly on my Dommy Racer. Another problem thrown up by using a mag. (The pulse comes from one plug)

Using a multimeter to detect whether a voltage is present or not or checking continuity is hardly rocket science. Having said that I remember chasing down a subtle fault where the meter showed I had 12 volts which was some sort of back feed via an LED.

I think I do know how to use a meter having done a technical apprenticeship with the CEGB and spent months in electrical and instrument fitters' workshops learning that amongst other things. Admittedly that was a long time ago and well before digital meters.

The main benefit of the Power Box is that it has a big capacitor so you can run coil ignition without a battery, or (if you disconnect the battery first) you can start the bike with a flat battery.  But since you now have the magneto, won't one of Al's regulators do all you need?

Hi Jacking this post to talk about multimeters...Yes Ian you might know a bit, but a lot of people believe they do but don't understand. The cheap digital multi meter will show a 'rubbish' display when trying to measure the Battery charge voltage (engine running) ignition interference! Then there is measuring 12V on ALL connections on a headlamp bulb, as the earth is open circuit.      We have a charge fault-new battery! I have been told. I have seen new batteries filled with distilled water only, and even reverse charged by the supplier. So watch word with faults, believe nothing check several times different ways. Try to understand what you are trying to do. Electricity easy stuff-you put put it into one end of the wire-it comes out the other end! Often very quickly!

... and use an old analogue meter for relevant tasks. I suppose the digital one is a bit like the cheap digital calipers - it's easy to use and readily readable unlike an analogue meter or micrometer. But all have their place.

Yes the BB power box regulates the alternator output to 14.5V (ish) but not through a Zener diode system. Regulator/rectifiers use controlled rectifiers, that produce the 14.5 more accurately and differently to the Zener principle. The aoservices Charge Lamp control unit is a small 3/4" device that tie wraps inside the head lamp. 3 wires to connect. Both the ao Charge Lamp and the BB Charge Lamp need an 'ignition' switch to switch the lamp off when not in use.