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If you are wiring up your Motogadget M Unit to your BMW Airhead and using an Acewell or Motogadget instrument and want the neutral switch to work this is the fix most of the time. No connection in gear.




Installing a Motogadget M Unit on your BMW Motorcycle?

Click here for a great "How To"


  • This article will help you wire the original Motogadget M Unit, M Unit Basic & Bluetooth to any 1970 to 1995 BMW 2 Valve Boxer(Airhead)

    We have noted where you need to use at least 16 gauge wire. Everywhere else we recommend 20 gauge or you can use the  Motogadget Wiring Harness.



    Once you have removed the main harness from the bike and the starter relay all that is left is the engine harness and the positive cable from the starter to the battery.


    On this harness you have the following:

    3 Pin Plug - for the voltage regulator. You will retain this. This is a good time to upgrade your charging system to a High Output Charging System.


    Short Black Wire - This goes from the starter solenoid to the “Out” side “Start” on the M Unit. Use 16 gauge wire to the M Unit.


    Long Black Wire - Negative terminal on the right hand coil. This is the signal wire to your ignition(points)


    Red Wire -  This goes to the main power lug on the M Unit. You will want to use an inline 8 amp fuse. Use 16 gauge wire to the M Unit.


    Blue Wire - This is the charging system light wire other wise known as the Generator Light. Without this hooked up your charging system will not work. You can use a standard 2 prong panel mount indicator light.(4 to 6 watt, 12 volt ) or you can use one of our “Charge Light Deletes”. Attach one wire to the blue wire on the engine harness and the second from the “AUX” on the M Unit.


    Handlebar Switches:

    We recommend using 3 switched per side.

    Right side - Start, Stop Horn

    Left Side - Left & right Turn Signal

    High Beam


    Running Individual Switch Wires:

    Each button will need to be grounded (this is the same if you are using the M Button). You can daisy chain them together own to one wire coming out of the handlebar. Depending on the diameter of the handlebar you want to drill a ¼” or 6mm hole to run the wires through.

    The other side of the switch will go to the “IN” side M Unit .


    Motogadget Color Code:

    Left Turn = Yellow

    Right Turn = White

    High Beam = Orange

    Starter = Blue

    Horn = Red


    M Button:

    If you decide to use the M Button we recommend running a few extra wires.

    Ground wire(black) from all of the switches to the bikes frame. 

    Kill Switch wire(grey) from the handlebar switch to the negative/minus on the right hand ignition coil.


    Ignition/Main Switch:

    You can use the Motogadget M Lock or a small switch hidden somewhere on the bike. A 2 pin switch is all that is needed. One wire from the battery to the switch(fused) and the other to the “Lock” on the M Unit.


    Kill Switch:

    The extra wire you ran from the handlebar switch to the negative side of the right and coil. This is also the same connection that gives a signal to the points or ignition unit (not where you are powering the ignition coil.


    Brake Light Switches:

    Most brake light switches work when the switch is pressed there is continuity between both terminals. With this said one side of the switch will go to ground and the other side to the “In”  side of the M Unit at the “Brake” terminal.



    Homs require 12 volt power on one side and a ground on the other. With the M Unit always acting like a ground wire it with the 12 volt power from “Aux” on the M Unit and the ground side to the “Horn” on the “Out “ side of the M Unit.


    “AUX” on M Unit

    There are many things on a BMW that require power when the bike is switched on. (switched hot) The “Aux” on the M Unit only allows one or two wires so plan ahead with a bus block or making a solder junction. Here are some of the things that require a switched hot

    Ignition coil, horn, tail light, neutral switch



    Ground wire to motorcycle frame

    High beam to “LIGHT HI” on the “OUT” side of the M unit

    Low beam to “LIGHT LOW” on the “OUT” side of the M unit

    If you are running a park light that will be wired to the “AUX” on the M Unit


    Ignition: From the “AUX” on the M unit to the + on the left hand coil


    Most aftermarket indicator lights like Motogadget Motoscope Minisign and Acewell have power to one side of the indicator lights going to “AUX” on the M unit and rely on a ground circuit to make them turn on.


    Neutral Switch:

    There is only one way we have found to make the neutral switch to work. Start with a Boxer Metal Neutral Switch. This is a 2 pole switch. One wire goes to ground and the other to the ground side of the neutral light. This seems to be true with Acewell Istruments & some Motogadgets.


    Oil Pressure Switch:

    Single wire that is the grounded side of the indicator light

    The other side of the light will need to be 12 volts


    Turn Signal Indicator:

    One side of the light will need to go to ground

    The other other side will come from the “OUT” side of the M Unit “TURN L” & “TURN R”


    High Beam Indicator:

    One side of the light will need to go to ground

    The other other side will come from the “OUT” side of the M Unit “LIGHT”


    See the M Unit instructions to configure the M Unit.

    Quick tip: You can tap a wire to ground coming from “CONFIG” on the “IN” side of the M Unit.


    We have done our best to be accurate in helping you. Please double check your work as we take no responsibility if you let the smoke out of the wires.


    There will be 6 wires going to the “AUX” on the M unit. We recommend you create a bus bar or secondary junction to connect these wires to the M unit.


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