Topic: Motogadget mUnit - CB750 Chopper wiring

[jphoto003]

Hey all, I have a 73 CB750 chop and I think I am almost done drawing up the wiring diagram with the motogadget mUnit for before getting busy. I have a santee box for it with a spring loaded key switch, I have a few question and was wondering if anybody on here can shed some light.

First question; What size fuse do you guys run for those with the mUnit?

Second question; What goes on the left terminal on the key ignition switch? Do I move the mUnit lock (out) to that position?

The way it is wired right now, the wire on the left terminal goes up to the headlight bucket and splits into the red wires on the speedo and tach. I've seen people wire their speedo and tach wires in the aux in of the mUnit.

Let me know what you guys think! Thanks, -J

[calj737]

From your key switch, you need only 2 wires: your "Orange" to battery +. And your "Black" should go to LOCK. The Black into LOCK activates the m-unit when the key is turned to ON/Acc as it is now sending switched 12v tot he m-unit. you can abandon all other wires from your key switch.

The AUX port is used to send "utility" 12v service to your gauge lights, tail light and license plate lights (if you're running those) and to your coils/igntion.

The "red" wire you have form the key switch should not be heading to START. The START port should take the input signal from your electric start button on the handlebar controls.

The Black wire from your R/R should also find its way to the LOCK port to monitor the 12v service thru your key.

Headlights and brake lights and indicators all are fed with 12v service on the right side of the M-unit outputs.

[jphoto003]

Hey @calj737 I don't have a start button on my handlebar, I have a spring loaded turn key switch meaning I start the bike like a car by turning the key in all the way. Let me know if you know what I mean by that.

And we are on the same page on the AUX part, just got my IGN system wired and also the gauge lights and running light will be on there as well.


Also forgot that I had a red wire running from selanoid to the start out. I added it on the diagram (red/green outline). Thats why I had the start in wired on the key switch(previous diagram). I just dont have an idea how the turn key switch works, my problem figuring out right now is how to activate the selanoid/starter when the key is turned in all the way for starting the bike. Is it the orange wire that goes to start in?


updated diagram below. Moved the bottom of key switch red wire to the battery (+) and the black wire from reg/rec to the 'LOCK'

[calj737]

Gotcha about your key switch. Missed that in the prior post. Can you post the model you have? It may be that the BLACK or ORANGE from your key needs to go to LOCK. Only way to tell is with a meter. Which has power only when switched? That's what should go to LOCK (I suspect your BLACK as its under spring load). From your current diagram, it looks to me as though ORANGE is unnecessary to the solenoid. What's your thinking as to why it should be connected? If you believe it to be the "start" impulse, it should go to START input on left, not the solenoid. And it should not have power to the START input, only GROUND. Measure its voltage with the key switched on (disconnect all solenoid/m-unit connections) leave BLACK to LOCK and then measure ORANGE. If its carrying voltage, it can not connect to START.

So either BLACK or ORANGE should be ground. If both are powered by the key switch, then omit the m-unit START ports altogether and simply wire the ORANGE to solenoid, but instead make the GR/RD a tie to chases ground. Then with the key you get power. BUT, you must be sure that the ORANGE doesn't stay powered after "ignition" else the solenoid will continue to spin with the motor running. Make sense?

Understand: the left side input on the m-unit only seeks GROUND inputs (with the exception of LOCK). So anything connecting there "grounds" the port and then transfers power to the right side (output) for switched 12v service.

Your START output to solenoid (RD/GR) makes better sense) if the above is true.

[jphoto003]

@calj737 Thanks for helping sort through this! A lot of good points on that last reply. And to start you're right about the orange, I don't know what part it actually plays. I got it from how my bike is wired originally when I got it. Looking at other diagrams online, I felt like it didn't need to be part of the wiring. I will check out the key switch and take some pics.

And with the left side of the munit only looking for GROUND, does that mean one pole of the key switch will have to connect to ground? I'm starting to think maybe the orange goes to start but yeah I just got more confused haha.

hmm...


Maybe seeing how my bike is wired without the mUnit will make more sense to kind of see where I got some of the wiring.

[calj737]

This latest diagram shows every each wire from your key being power, not ground. If so, ORANGE does NOT got to START nor to Ground. The Gr/Red you had wired, take that to GROUND and leave ORANGE to solenoid. You're bypassing the m-unit START function, but that's fine.

[jphoto003]

@calj737 could it be possible that it is getting grounded through being mounted on the electrical box or the chasis?

Im at the airport now and wont be back to my bike til wednesday, on the meantime I'm still online looking at other peoples wiring diagram and came across this one. It looks to me that I am running the same key ignition switch. And it looks like the middle terminal on the key switch is labeled 'str' im assuming the start impulse?

[DaveBarbier]

On my 550 I'm using a 15amp fuse for the m-Unit. But I have my reg/rec wired directly to the battery (not tied in to the m-Unit power source like you) and that has a 30amp fuse.

[calj737]

J - That diagram clearly shows ORANGE as leading to the solenoid, which would be power, not ground, as there is a separate  wire form the solenoid to ground (their thin red tied to green). I believe you'll bypass the m-unit START with that key switch is all. Its not a big deal in the end.

But I've never seen a key switch that uses a separate GROUND wire because, as you suspect, the housing of the switch grounds it to the chassis.

I'll be around mid-week, so when you get back, send me a PM or post up here and I'll check in. Travel safely-

[scottly]

Let me know what you guys think! Thanks, -J

Why are you using an expensive, complicated M-unit on a simple chopper wiring system??

[jphoto003]

@calj737 yeah, I think I'm gonna start diving in the wiring when I get back just to get an idea on whats what. Thinking about unhooking the orange on the key switch, and see if the starter is activeted when turn the key in to start. We'll see. Thanks again will check back in when I get back home

@scottly because why not? Haha I didnt get the munit brand new and i have a few tricked out ideas on lightings i think the m unit will help out. Im not feeling the birds nest in the headlight bucket.

[calj737]

I wouldn't do that... First, you need to check every wire with a meter from the key switch while the key is hooked to the battery and nothing else. If each has power at some key position, then nothing goes to the m-unit START. Only the line that is active and switched with the key in the "run" position should go to LOCK.

[jphoto003]

Took your advice on this one @calj737 and I took the key switch and used a multimeter to see the flow of electricity on the key switch.

As suspected, the orange wire that is connected to the solenoid is the start impulse wire. Took a video below of me going through the key ign switch. Also have an updated diagram, keeping in mind what @davebarbier said about his fuse set up.

Let me know if you guys think this latest diagram makes sense. Also do I just leave the accessories pole open without any connection?

Thanks so much, you guys are a big help!

The birds nest inside the box (Theres also a nest in the headlight bucket)

[calj737]

So you confirmed that indeed the STR on the key switch sends power which is exactly why you DON'T connect it to the m-unit START. Connect the STR (ORANGE) directly to the solenoid, and make sure you provide a GROUND on the solenoid.

To remind you: the left side of the m-unit CAN NOT accept power, only GROUND signals. If you do, you'll cook the m-unit (or at least get smoke  until the port fault resets.).


Your birds nest is heavily altered by the PO. I would ditch that terminal block altogether. Don't use those cheap blue "crimp on" style of connectors; they're crap. Everything should be in weather tight connectors, properly soldered and crimped where appropriate to deal with weather exposure.

[jphoto003]

@calj737 so just to get it clear this time around, I have to bypass the m unit start if I wanna use the key switch to start the bike. And the only way I'll be able to use the m unit start is if I use a separate momentary push button to activate my starter?

noted on the cheap connectors!

[calj737]

You understand correctly.

[jphoto003]

Finished wiring and fired up on first pass.

Here's the video of me starting the bike. https://www.instagram.com/p/BEAeHXLCHK9


below are two versions of using the motogadget m-unit for your cb750. Thanks a lot for the help @calj737


This wiring diagram is what worked for me, by keeping the turn key switch. By passing the start function of the mUnit. Another version of the diagram under this one which is set up to use a push start button which uses the mUnit start function. Hope this helps in the future!






This version is for using a push button.