I have been planning on updating the wiring on my BMW K75 to remove the standard controls fuse box etc and have chosen to do this by adding a M-Unit from Motogadget. The controls will be replaced with M-Buttons and the Speedometer/tach has been replaced with a KOSO T&T multifunction gauge. 

There are multiple examples of people adding a M-Unit to their K bikes, but the documentation is next to none, which is why I have made my own. I am posting this here to hopefully help others who are interested in a similar solution. Here you can see the wiring diagram that I have created for this solution. WARNING: This wiring setup has not been tested so if you want to use it please do this with caution, or wait until I have modified my system so I can tell you if there are any problems with the design.



If you need a larger version of this file please PM me. Also if there is anyone out there that sees an immediate problem or has questions please contact me.

Hope this post will be helpful for your project.

I'd be very interested to hear how things work using the M-Unit.  Please keep the forum posted (or just me if nobody else is interested)

I looked at this some time ago and I saw that in certain circumstances, the M-Unit can be used instead of having a separate starter relay.  Your diagram has a starter relay though.  Do you know if it's possible to forego the starter relay on a K75/K100?  Having experienced the famous welded relay situation, I'd love a solution that involved ditching the starter relay.

I attempted the M-Unit a while back, got everything working before I wired the starter switch. After that the thing caught fire. scariest moment of my K-life so far. After talking with Motogadget, they decided it was a faulty unit, but never tried it again
Hope it works for you

Yikes! I guess even with high end stuff, a bad one gets through once in a while.

I'm curious, did you use the starter relay? What about the load shed relay? The diagram above doesn't have one, and I'm wondering if there are issues with not having it.

I kept the load shed for the parts that need it. I cant remember about the starter relay. I know the fire happened at the positive battery connection terminal, so i am assuming that was a faulty connection in there somewhere

Thought I'd keep this alive with my thoughts/experiences in case anyone else is looking at using the m-unit.

I'm in the research phase - looking at the main wiring diagram over and over again until it sinks in and I can make heads and tails of the inter-dependencies and complexities.

I want to use the Motogadget m-unit and m-switch mini to simplify the wiring and get rid of the big old ugly OEM handlebar switches.  I'm also planning to remove the Bulb Monitoring Unit, Flasher Unit, Horn Relay, Load Shed Relay, and Fuse Block, along with the Anti theft connector and Special Equipment Connector.  Oh, and the big old clunky OEM handlebar switches!

From what I understand you still need to use the starter relay, but I don't understand how the m-unit knows how long it should supply power to the control coil of the start relay (meaning until the engine fires).  The m-switch sends a momentary contact to the m-unit when you press the start button, not the same as the OEM switch that you hold closed for as long as it takes for the engine to fire.  I understand that the ground to the coil in the starter relay is controlled by the ICU, and the ICU will remove the ground once engine speed goes above 700 RPM.  The m-unit sends power from the "Start Out" to the control coil of the start relay.  There must be some smarts in the m-unit so it knows that the engine has fired, but I'm yet to learn how this works.



Regarding the load shed relay, I think this can be removed.  From Bert's diagram below, the load shed relay cuts power to:

1. Lights
2. Horn Relay
3. Flasher Unit
4. Temperature Switch unit

The m-unit will automatically cut power during startup to the lights, flashers, and horn, which leaves the Temp Switch unit, which I believe would be isolated to prevent the fan from starting during a hot engine start.  The 12V Green/Brown wire to the Temp Switch Unit, coming from the Horn Relay, from fuse #7, from the Green/Blue wire from the output of the load shed relay, could be wired to the "Light Lo" output of the m-unit, and this output be configured to be always on (except of course when the start button is pressed).

That's my understanding so far, but more research to be done 

Zach sent me over his full size wiring diagram tonight, and it looks bloody brilliant!  Exactly the kind of simplification I was hoping to achieve.  The only stray from original function in terms of the Load Shed Relay that I can see is the Aux Out on the m-unit is supplying power to the Green/Brown wire that runs to the Temp Switch Unit during start up, where as the Load Shed Relay would normally isolate this supply during start up.

Looks like no clutch switch or neutral switch to interfere with starting.  The neutral relay emulator board is there to provide a neutral light for the dash.

Fantastic work Zach!   

Now I'm just waiting to hear if he's used this set up and gone for a ride 

Hello Zach and others setting up there k bike with the munit. Zach great work on wiring diagram . Can you send me I high resolution file? Also, has any one successfully got the wiring configuration to work? Any input would be greatly appreciated ! Thanks Michael

simpsonk100 wrote:Hello Zach and others setting up there k bike with the munit. Zach great work on wiring diagram . Can you send me I high resolution file? Also, has any one successfully got the wiring configuration to work? Any input would be greatly appreciated ! Thanks Michael

No one has reported back on whether or not their bike catches on fire with this as of yet 


It looks good to me but I'm not an auto electrician and haven't started sorting out my wiring.  It's for the K75 but apart from the missing cylinder looks like an easy swap for the K100.

I've hosted it so I think you should be able to download it.

https://drive.google.com/open?id=1OsEEKz-IGU5K4YCM8C0w0rMpGC3xcnVf

Cheers,
Nods

These schematics are awesome!  Have a new gauge and m-unit I need to wire in. I'll be doing it over the next month, I'll try to take pictures to post back to the forum and let you all know how well it works. 

FYI, you should be able to use the starter relay in the M-unit itself and his should remove the issue of low voltage welding of the starter relay when the bikes battery is low. I'll confirm once I've made it work, but my research indicates it should be just fine. Can't wait to get rid of the fuse box, already had one issue in there with a relay causing issues. Don't need any more. 

Asp will be adding a LED and resistors to excite the alternator if anyone has any suggestions on that. With the gauge cluster replacement this is a requirement. 

If anyone is in the Boston area and wants to see or help let me know. I have a lot of fabricating to do in my spare time to get the pile of parts I have on the bike.

Unwrapping, testing continuity, working out the rewiring and deciding where to put BACK the items that have to stay, rewiring the bike is NOT fun.

The diagram is useful but packaging things back up neatly is still no joke.  Going to have to find a good way to hide the wiring.  Doesn't make it any easier that I'm also redoing the gauges with a motoscope pro.

Stick at it, you'll be right.  Are you re-dong the loom, as in unwrapping it all to remove redundant wires and add new wires to the main loom?

nods wrote:Stick at it, you'll be right.  Are you re-dong the loom, as in unwrapping it all to remove redundant wires and add new wires to the main loom?

I am pulling apart the loom currently and trying to consolidate wiring. I'm also seriously looking at replacing be stock brake and clutch levers then custom machining new housings for my switches and using some ip67 waterproof buttons and switches to replace the stock ones. Just trying to decide how crazy I get. 

The problem with the loom as is is that if I leave it together I'll have a ton of extra wires just taped off. If I take it apart I run the risk of screwing up something for fuel or things like the temp sensor. Just going slow and labeling it all right now as I slowly work things out.

So a few things learned.  

1.  M-unit requiring grounded switching on the trigger side makes this a PITA on the K100.  For example the starter.  Net result, unless you really love the existing controls, expect to replace them or spend significant time rewiring the switches nicely to make this work.

2.  The wiring diagram provided needs to be used with a grain of salt.  For example it missed the power into the ignition switch. I reversed the ignition switch wiring from the diagram, fed power into the red wire and used the green wire for the trigger on the M-unit.

3.  Take your time and label EVERY WIRE.  I had to make some small changes, if I didn't have EVERY WIRE I cut tagged, it would have been a nightmare.

4.  Have a good continuity checker and make sure you have your grounds in good shape/tight.  Caused some of my own consternation just by having some poorly hooked up grounds.

I'm also doing a Motoscope pro at the same time so my wiring headaches are even larger.  Had to buy a board to smooth the speedo input and figure out how and where to locate these items.

Overall it's doable but it's taken me 2x as long as I thought it would and I'm probably only halfway done.

Thanks for the update.  Always going to be a big job to re-do the wiring 

Ardinos wrote:So a few things learned.  

1.  M-unit requiring grounded switching on the trigger side makes this a PITA on the K100.  For example the starter.  Net result, unless you really love the existing controls, expect to replace them or spend significant time rewiring the switches nicely to make this work.

2.  The wiring diagram provided needs to be used with a grain of salt.  For example it missed the power into the ignition switch. I reversed the ignition switch wiring from the diagram, fed power into the red wire and used the green wire for the trigger on the M-unit.

3.  Take your time and label EVERY WIRE.  I had to make some small changes, if I didn't have EVERY WIRE I cut tagged, it would have been a nightmare.

4.  Have a good continuity checker and make sure you have your grounds in good shape/tight.  Caused some of my own consternation just by having some poorly hooked up grounds.

I'm also doing a Motoscope pro at the same time so my wiring headaches are even larger.  Had to buy a board to smooth the speedo input and figure out how and where to locate these items.

Overall it's doable but it's taken me 2x as long as I thought it would and I'm probably only halfway done.

Thanks for your feedback, 
1. This diagram is shown using different controls for just this reason you stated.
2. Power to the ignition? Please elaborate, the ignition switch is just that a switch, the power is supplied to the m unit and when the the switch is turned on the remaining accessories receive power.

As i stated before this is just a reference that is so far untested by me. So if you see any problems with it please PM me directly. 

Good luck

So the only relay that is used is the fuel injection relay? My understanding is that the munit will eliminate the rest of the old relays

Okay, munit tricks. Be smart, pay attention to what triggers on the M unit want switch to ground. I had for example power switched through the rear brake rather than ground. Net result, rear brake switch didn't work. (Interesting side note, bike would be killed by rear brake and any flasher or change of gears, same behavior as  if you hit the confit switch while riding. You have to then switch the bike off then back on and restart it)   Fixed that, then found issues with setup, start the bike, flasher cancel was hooked up working as a kill switch. Grrr. Make sure you wire things with LABELS. can't emphasize how much time I saved with good labeling to my wires. 

So ignition switch needed to be rewired. Controls totally re wired. Basically I rebuilt the harness. If you are faint of heart and don't get electricity, don't try this at home. 

For example, I had to setup 3 relays to get switch to ground working for my neutral indicator. What a pain. Wired it the first time switch to power, whoops, motoscope pro gauge was expecting switch to ground. Grrr. 

Anyways I have started and ridden the bike. Only thing now is trying to figure out the correct speedometer impulse setting and some other minor stuff.

For the Motoscope Pro with a BMW K100 and the speedometer smoothing circuit in place, your impulse width is 6 ImpW in the settings. That was fun to trial and error to figure out.

I have three relays. Temp sensor, fuel injection and starter. You may end up with something else depending on the route you take but for the starter it takes a lot of amps and I didn't bother to remove the relay for that.

Since Last thing, the wiring diagram on here, was a GODSEND. While it still took some interpretation and minor modification to make everything work, it definitely helped me out a TON. With just the Clymer manual it would have taken me 10x as long to sort it all out. Thank you smart forum people. If anyone is hooking up an Munit or Motoscope Pro to an old BMW K100 and needs advice. Let me know. Glad to help out.

Anyone have the high res version if this wiring diagram? Looking to add an m-unit to my bike in the comming months and would love a chance to take a look and get my head around how it all goes together.

Thanks

Sooprvylyn wrote:Anyone have the high res version if this wiring diagram?  Looking to add an m-unit to my bike in the comming months and would love a chance to take a look and get my head around how it all goes together.

Thanks

Does this work:
https://bikebrewers.com/motogadget-m-unit-wiring/

jmccrary wrote:
https://bikebrewers.com/motogadget-m-unit-wiring/

Here's a link to one man's efforts with the M Unit < click there

zach_ross, any chance I could get a high resolution copy of your m.unit wiring diagram I would also like to retrofit my bike with m.unit. Thanks.

Just trying to figure out the need for the starter relay with the m-unit blue.

The m-unit blue can supply 30A from the Start output.  Is this enough to wire directly to the starter motor?  Or should there still be a starter relay between the m-unit and the starter motor?

I'm also a bit confused by the term "starter solenoid".  Our starter motor does not have an integrated solenoid right?  It uses a sprag clutch to engage the starter motor with the flywheel - is that how it works?

Cheers,
Elliot

Their 'starter solenoid' is our 'starter relay'. AFAIK the difference is that a relay has a pivoting arm and makes across one contact, whereas a solenoid simply slams a bar across two contacts. For the purposes of wiring they can be thought of as the same and no, 30 amps is not enough to handle the starter motor. You will need to use the m-unit to operate the starter relay which, in turn, will spin the starter motor. The 30 amp output from the m-unit must be wired to pin 30 on the starter relay. Pin 30 must be disconnected from the battery (the red wire)  as that power feed will now be redundant.

Dai wrote:Their 'starter solenoid' is our 'starter relay'. AFAIK the difference is that a relay has a pivoting arm and makes across one contact, whereas a solenoid simply slams a bar across two contacts. For the purposes of wiring they can be thought of as the same and no, 30 amps is not enough to handle the starter motor. You will need to use the m-unit to operate the starter relay which, in turn, will spin the starter motor. The 30 amp output from the m-unit must be wired to pin 30 on the starter relay. Pin 30 must be disconnected from the battery (the red wire)  as that power feed will now be redundant.

You're a champ Dai, thanks a lot mate.  Crystal clear.

Almost. I can think of one possible thing wrong with my reply and it depends on the answer to the following question. Does the m-unit require you to wire the starter button to it? If so, there's a different fiddling you need to do around the starter relay. Contrary to yesterday's reply, in this case leave pin 30 connected to the battery (red wire) and connect the m-unit 30amp output to pin 86 (black/yellow). Leave the black/yellow connected to the relay.

Guess who has no experience of m-units

[Edit] Just checked the K75 diagram - the above info is correct. Sorry about the screw-up yesterday

Thanks for this Dai, I somehow missed your reply.  Yep, connecting the black/yellow to the m-unit Start output is how the OP has it wired in his diagram.

I won't be using the OEM switches.  The motogadget switches supply a small signal current to the input side of the m-unit when pressed.  This tells the m-unit what to do on the output side.  That original diagram by zach_ross is still looking pretty good for my purposes, even though it's missing a cylinder!

Well...I started today just untaping the harness and figuring out what does what.  Any suggestions on how to get started with cutting away the wires lol??  I am a bit nervous...but looking forward to it.  

Does anyone live in the Orlando/Daytona area that has done this before?  I know I can do it, but never hurts to have someone who did this before help out!

Does anyone have a larger version of this diagram they can send me? I've tried to contact the OP but with no luck so far. Thanks in advance!

My post above on March 10 has a link that looks to be still working

Thanks Nods, sorry I didn't spot that, much appreciated 

No worries, good luck. Let us know how you get on