Ajs Matchless Lightweight 12V Conversion Repair Guide

Difficulty

Moderate

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Time Required

                          2 hours

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AJS/Matchless Lightweight 12V conversion
6 steps

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Introduction

The Wipac alternator is a two-phase, 60W affair. You can connect the three output wires straight into a three phase rectifier. This will work just fine (and has the advantage that you don’t need to puzzle out which alternator wire is which…).

The only downside of this 12V conversion is that you will lose the “EMG” feature that allows you to start the engine when the battery is flat. However, the greater reliability of the electronic charging system should mean that you won’t miss it.

Read on for more information…

Step 1

              12V conversion parts

You will need the following parts to convert your bike to 12V:
12V 4Ah battery (e.g. YTX5L-BS)
Rubber battery strap
10A in-line fuse and a selection of crimp or solder terminals
A single-phase (2 wire) or 3-phase (3 wire) 12V regulator rated at 150W or more. A-Reg, Wassell or Podtronics all fine)
12V 4 ohm ignition coil
12V bulbs
12V horn (optional)

You will need the following parts to convert your bike to 12V:

12V 4Ah battery (e.g. YTX5L-BS)

Rubber battery strap

10A in-line fuse and a selection of crimp or solder terminals

A single-phase (2 wire) or 3-phase (3 wire) 12V regulator rated at 150W or more. A-Reg, Wassell or Podtronics all fine)

12V 4 ohm ignition coil

12V bulbs

12V horn (optional)

1024

Step 2

              Check your alternator stator

The alternator stator is supposed to be insulated from earth.
Unfortunately, as the stator insulation degrades, the coil can become connected to earth. If this happens it will destroy your shiny new electronic regulator. The insulation in the picture is visibly damaged and eventually caused a short circuit…
So, check the stator windings are free of earth with a resistance check.
Disconnect the three alternator wires and check the resistance from any wire to earth. You should see a reading over 10k ohms.

The alternator stator is supposed to be insulated from earth.

Unfortunately, as the stator insulation degrades, the coil can become connected to earth. If this happens it will destroy your shiny new electronic regulator. The insulation in the picture is visibly damaged and eventually caused a short circuit…

So, check the stator windings are free of earth with a resistance check.

Disconnect the three alternator wires and check the resistance from any wire to earth. You should see a reading over 10k ohms.

Step 3

              Remove the 6V parts

The 12V system is quite a bit simpler than the Wipac system, as there’s no longer a need to switch the alternator output with the headlight. It’s probably easier to refer to the differences in the wiring diagram pictures to see what needs to be removed…
The traditional conversion uses a single phase (two wire) regulator by joining the orange & light green wires. My diagram shows a 3-phase (three wire) regulator connected to the three alternator wires, which will also work just fine.
Disconnect and remove the 6V battery. Note the brown wire that went to the negative terminal; we’ll be connecting the 12V battery positive terminal to it later (via a 10A fuse).
Disconnect and remove the rectifier, noting the brown wire that went to the rectifier negative terminal (you’ll be connecting the 12V regulator to this wire later…)
Remove the orange, light green and white wires, as well as the resistance wire, from the main loom
Remove the 6V ignition coil
Remove the headlamp bulb, sidelight bulb, stop/tail bulb (and any other 6V bulbs)

The 12V system is quite a bit simpler than the Wipac system, as there’s no longer a need to switch the alternator output with the headlight. It’s probably easier to refer to the differences in the wiring diagram pictures to see what needs to be removed…

The traditional conversion uses a single phase (two wire) regulator by joining the orange & light green wires. My diagram shows a 3-phase (three wire) regulator connected to the three alternator wires, which will also work just fine.

Disconnect and remove the 6V battery. Note the brown wire that went to the negative terminal; we’ll be connecting the 12V battery positive terminal to it later (via a 10A fuse).

Disconnect and remove the rectifier, noting the brown wire that went to the rectifier negative terminal (you’ll be connecting the 12V regulator to this wire later…)

Remove the orange, light green and white wires, as well as the resistance wire, from the main loom

Remove the 6V ignition coil

Remove the headlamp bulb, sidelight bulb, stop/tail bulb (and any other 6V bulbs)

Step 4

              Fit the 12V battery & regulator

Fit the regulator somewhere convenient (above or below the coil is a good option)
Fit the new 12V battery. The widely-available 4Ah YTX5L-BS fits in the existing tray just fine. Use a bit of foam to isolate the battery from the engine vibration and a rubber strap to hold it in place.
Connect a 10A inline fuse to the battery positive lead and connect the other side to the brown wire that previously went to the 6V battery negative terminal (for negative earth)
To use a single-phase regulator, you need to join the orange and light green alternator wires and connect them to one of the yellow regulator wires. The white alternator wire goes to the other yellow regulator wire. To use a 3-phase regulator, connect the yellow wires to the three alternator wires. It doesn’t matter which one goes to which.
Connect the black wire from the regulator to earth (for negative earth)
Connect the red wire from the regulator to the brown wire that previously went to the rectifier (for negative earth)
Connect the battery negative terminal to earth (for negative earth)

Fit the regulator somewhere convenient (above or below the coil is a good option)

Fit the new 12V battery. The widely-available 4Ah YTX5L-BS fits in the existing tray just fine. Use a bit of foam to isolate the battery from the engine vibration and a rubber strap to hold it in place.

Connect a 10A inline fuse to the battery positive lead and connect the other side to the brown wire that previously went to the 6V battery negative terminal (for negative earth)

To use a single-phase regulator, you need to join the orange and light green alternator wires and connect them to one of the yellow regulator wires. The white alternator wire goes to the other yellow regulator wire. To use a 3-phase regulator, connect the yellow wires to the three alternator wires. It doesn’t matter which one goes to which.

Connect the black wire from the regulator to earth (for negative earth)

Connect the red wire from the regulator to the brown wire that previously went to the rectifier (for negative earth)

Connect the battery negative terminal to earth (for negative earth)

Step 5

              Fit the rest of the 12V parts

The lights, coil and horn should all be changed for 12V items. Make sure the new coil is connected the right way round: the “-” terminal should be connected to the maroon wire that goes to the points (assuming negative earth)
There’s no need to change the condenser if you are sticking with the Wipac points ignition.
If you wire the system for negative earth, then you can use widely-available LED bulbs
I tried two different LED headlamp bulbs. They were nice and bright, but both failed after a few months due to the cooling fan breaking. I’d recommend only using fanless LED bulbs. I have since found that the alternator has enough output to power a proper 55/60W H4 halogen, so I just use one of those.
If you are using negative earth, then don’t forget to swap the wires to the ammeter, otherwise it’ll read backwards

The lights, coil and horn should all be changed for 12V items. Make sure the new coil is connected the right way round: the “-” terminal should be connected to the maroon wire that goes to the points (assuming negative earth)

There’s no need to change the condenser if you are sticking with the Wipac points ignition.

If you wire the system for negative earth, then you can use widely-available LED bulbs

I tried two different LED headlamp bulbs. They were nice and bright, but both failed after a few months due to the cooling fan breaking. I’d recommend only using fanless LED bulbs. I have since found that the alternator has enough output to power a proper 55/60W H4 halogen, so I just use one of those.

If you are using negative earth, then don’t forget to swap the wires to the ammeter, otherwise it’ll read backwards

Step 6

              Test it

Switch the headlight on. The ammeter should show discharge. If it shows positive charge, you need to reverse the ammeter connections.
Switch the headlight off, put the ignition switch to “IGN” and start the engine as usual
The ammeter should show positive charge
Switch on the headlight. The ammeter should still show positive charge.
Check the horn and brake lights. Everything should work as normal.

Switch the headlight on. The ammeter should show discharge. If it shows positive charge, you need to reverse the ammeter connections.

Switch the headlight off, put the ignition switch to “IGN” and start the engine as usual

The ammeter should show positive charge

Switch on the headlight. The ammeter should still show positive charge.

Check the horn and brake lights. Everything should work as normal.

Now you can enjoy easier starting and brighter lights!

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                    Paul Barnfather

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Terence Grinnell - Nov 30, 2022

Hello there, Can you help me please, I have just had my AJS 350cc Converted from 6volt to 12volt with a wipac system. It is now a 12volt positive but with the 10 amp fuse fitted to the negative terminal is that correct.

Paul Barnfather - Nov 30, 2022

Yes, that sounds correct. If it’s positive earth, then the fuse should be in the negative line from the battery.

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