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THE REVIVAL APPROACH TO WIRING AN M-UNIT
"The map may not be the territory but it sure helps a lot"
The m-Unit is light years ahead of any other power distribution module on the market and the best thing to come to motorcycle electrical restoration ever Hands down. Installing one is no small task; if it's your first m-Unit installation and you are not well acquainted with the OEM electrical system you might expect to spend a minimum of 50-60 hours on this project. So we've put together a series of articles and diagrams to help streamline the process for you.
In my experience it usually isn't that difficult to get the wires to connect from the correct things and make the system work, the difficulty comes in making it all as simple as possible while looking perfect. If you invest time in the beginning to familiarize yourself with your factory electrical system along with the m-Unit and then map out your installation you'll have some familiarity with the territory before you ever set foot on land.
Minimum required for the task:
1 A legible, accurate, OEM wire diagram
3 Wire to build your new harness
4 Main fuse holder
5 Complete charging and ignition system components
6 Wire loom or tape
7 Heat shrink
8 Crimp tools, Solder, and solder iron
the same but different
Nearly all carbureted bikes are going to follow the same basic wiring, with a few exceptions such as convoluted tour bikes or the era just before fuel injection was introduced. The main differences in most instances will be your OEM ignition and charging system wiring and whether you choose to use kickstand switches, kill switches, charging lights, etc.
There are in some cases more than one way to go about wiring certain elements of the m-Unit and have everything still function. Whether you follow our methods or someone else's you should try your best to make sure all positive power wires are metered by the m-Unit's circuit protection or an added fuse.
How do you eat an elephant? One bite at a time...
Best Practice is to break this down into bite-sized pieces. Print out multiple copies of your OEM diagram and on each one highlight a different portion of your system on each page. Start with just one part, the headlight circuit for example, and knock that little bit out before moving on to the next. Doing it this way makes it a lot easy to wrap your head around it and easier to retrace your steps should something need debugging.
One tip for making it easier is to use a highlighter to mark just the wires that connect to the ignition system. For the first pass, don't highlight down the branch circuits, and try to only focus on the wires are connected from "A" to "B" points, most of the wires in the ignition system will be connected this way, and you will come back to the branch circuits later. Once you have all the "A" to "B" circuits identified, you can determine what is going on with the circuits that branch and have multiple connections. On carbed bikes it is most likely that you have a positive connection that supplies power from the ignition switch and a ground wire that ties into the chassis. On Fuel-injected bikes, it is a bit more complicated with the fuel pump relay and the sensors, but following along with this method you should be able to isolate the system in the diagram and identify the switched power connections that need to be powered with the "AUX" output.
You can use the blank template included with our Universal m-Unit Wiring Diagram to trace out the various systems of your new wiring harness.
It helps me to understand how the m-Unit integrates into the system by breaking the wiring up into 3 subsystems.
- Charging - This consists of the wiring from your magneto or stator, Reg/Rec and battery. The better part of this system will remain unchanged. If you have an old system with a separate regulator and rectifier or your Reg/Rec is 20+ years old it is time to replace it with a quality modern component. The materials in older Reg/Rec's have a shelf life and are well past the expiration date. The Reg/Rec deals on eBay/Amazon are often too good to be true and the lack of quality control may cost you more down the road. If you are installing a Lithium battery of any kind you need a lithium optimized Reg/Rec which you can find on our site.
WHAT YOU NEED TO DO. Using your OEM wiring diagram, trace the wires back from the Regulator Rectifier, Determine which wire provides Rectified 12v+ power back to the battery this wire will need to have the Main fuse between the Reg/Rec and Battery. Do not get confused by the Motogadget diagram where the 12v+ power to the m-Unit branches from the same Reg/Rec wire to the battery. The 12v M-Unit terminal can be wired directly to the battery or spliced with the Reg/Rec to battery wire, the results of both methods are the same.
- Ignition - This is your Points, Black Box, ECU whichever you have, and your coils, etc. For most ignition systems the only amendment to the wiring will be to route the 12v+ power wire that supplies the ignition system will be installed in the AUX (m-Unit V.2) or Ignition OUT (m-Unit Blue/Basic). One exception to this is if you have a CDI ignition. If you're not sure if you have a CDI ignition you can find instructions on how to determine what you have in our CDI X m-Unit Article.
WHAT YOU NEED TO DO. To wire a stock ignition system with the m-Unit, you need a clear and correct wire diagram for your bike. The basic plan is to keep the OEM system intact and simply supply power from the m-Unit "ignition" output. Start by identifying the spark plugs or coils in the diagram and trace their connections back to the ignition control module or points and then on to any devices connected to it, making note of any connections that are powered from the ignition key switch. Follow the branches and get an understanding of what is connected to what, usually this includes kill switches and safety switches. Any connections to the engine sensors, pulser, or trigger coils should be maintained as original, and the only changes that need to be made are connecting the power feed wires to the m-Unit "Ignition Out terminal".
- Ancillary (m-Unit) - The m-Unit acts as a brain that controls voltage for everything on your bike aside from the charging system. This subsystem also includes all of your lighting, switches, and anything else that has an assigned input or output on the m-Unit.
Electronic Fuel Injected bikes (EFI) -
Note: Carbureted bikes are generally going to be much easier to approach than a fuel-injected bike. Rewiring an EFI bike is a big project, no way around that. But after you get through it you will have a much better idea of what all the bits and pieces are, and realistically it isn't that difficult, it just takes a lot of time and patience. The big issue with many modern bikes is the ECU / Gauge / Immobilizer / Red Key situation. On all our EFI Ducati builds we end up replacing the ECU with an aftermarket module that is more programmable and eliminates the security system. The bottom line is that in many of these scenarios you can't replace the gauges without solving the immobilizer problem, and we are not aware of a cheap solution.
The biggest tip I can give is to pick one thing at a time and work it out, i.e. TPS sensor, get that connected, then Oil temp sensor, then starter solenoid, etc. By working through one at a time it isn't as overwhelming. If you work from the sensor back to the ECU you can get the routing and cable lengths just right, and then re-crimp with new terminals and install back into the connector.
If you aren't relocating electrical components you might be able to leave the main factory loom for the ECU/EFI mostly intact and just clean up the rest of it. But if you really want to get it down to bare bones you'll want to start from scratch.
A Few Final Notes:
Grounds - It is of vital importance that ground connections be stripped of paint and have a clean, uncorroded, uninterrupted path to ground. Handlebar button/switch grounds should be tied together and a single wire run back to the m-Unit Main ground.
It is not a bad idea to run most/ all grounds back to the m-Unit main Ground location to ensure they all have ideal continuity.
Gauge & Indicator lights - The m-Unit handles power distribution, and control, so it doesn't really affect much with the gauge and warning lights. Those remain basically the same as stock, with one exception, the power comes from the "AUX" output. This means the oil pressure light gets power from the m-Unit and then the switch is the sensor on the engine which closes the circuit when the oil pressure is too low. Basically the neutral light and oil pressure light use a switched ground configuration, and the high beam and turn signal indicator uses a switched positive configuration. See our m-Unit wiring diagrams for a visual explanation.
Wired control switches - DO NOT have power flowing through them. Do not connect these to 12v power. This includes brake switches. The m-Unit is a micro-controller, it reads ground signals sent by a momentarily pressed button and turns on the associated function. This is fundamentally different from all OEM controls. You have 2 wires, one goes to ground, the other goes to the m-Unit input.
How the AUX 2 Fan Delay works - Choosing this option in the setup menu will program the AUX outputs to come on along with the Ignition when you switch the key to the on position or otherwise turn the bike on. When the ignition is cut off the AUX 2 will maintain power in order to continue cooling the engine for 120 seconds after then shut itself off.
DOCUMENT YOUR WORK!!!! - I can’t stress this enough, do it every time you work on the bike. Keep notes of what you’ve done. Keep documentation for all of your components, wiring diagrams, and notes. You will not retain all of this in your memory and down the road will all be vital information for either you or the new owner.