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Author Topic: M-unit wiring diagrams for SOHC/4 bikes  (Read 756 times)

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Offline theDQG

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M-unit wiring diagrams for SOHC/4 bikes
« on: July 25, 2019, 04:10:00 am »
I am working on a wiring diagram for my CB750 k4 featuring a M-unit blue, M-lock, etc.

I would like to invite everyone to post their M-unit wiring diagram(s) in this thread for purpose of sharing information or assistance.

I will share mine once it is done and reviewed for corrections.

Thank you in advance.
'83 xv920
'76 xs650
cb750 k4 (2)
'81 R100RS

DQG = The Dumb Question Guy. I ask dumb questions all the time. Bike over ego.

Offline calj737

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #1 on: July 25, 2019, 06:59:01 pm »
Go nuts
'74 550 Build http://forums.sohc4.net/index.php?topic=126401.0
'73 500 Build http://forums.sohc4.net/index.php?topic=132935.0

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Offline theDQG

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #2 on: July 26, 2019, 07:02:45 am »
I found this:

'83 xv920
'76 xs650
cb750 k4 (2)
'81 R100RS

DQG = The Dumb Question Guy. I ask dumb questions all the time. Bike over ego.

Offline Jnel

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #3 on: October 19, 2019, 08:07:37 pm »
This is mine.

Sent from my SM-N950U using Tapatalk


Offline roach374

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #4 on: November 25, 2019, 11:28:03 am »
Go nuts

In your diagram, what do the circles with "M", and "G" in them represent? (Sorry if this is a dumb question).

Offline calj737

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #5 on: November 25, 2019, 04:28:20 pm »
Go nuts

In your diagram, what do the circles with "M", and "G" in them represent? (Sorry if this is a dumb question).
G is a reference to the Stator/alternator (oft referred to as “Generator”)
M is a reference to the Starter Motor (you know, the thing that makes the bike work under electric start)

Not dumb questions, just “new to electrics” questions  :)
'74 550 Build http://forums.sohc4.net/index.php?topic=126401.0
'73 500 Build http://forums.sohc4.net/index.php?topic=132935.0

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Offline roach374

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #6 on: November 27, 2019, 02:50:35 pm »
Go nuts

In your diagram, what do the circles with "M", and "G" in them represent? (Sorry if this is a dumb question).
G is a reference to the Stator/alternator (oft referred to as “Generator”)
M is a reference to the Starter Motor (you know, the thing that makes the bike work under electric start)

Not dumb questions, just “new to electrics” questions  :)

Thanks!

One more question: In some wiring diagrams, I see the m-Unit's IGNITION output powering an ignition coil, and in others it's not. Which is "correct"? (Keeping in mind that my bike has TWO ignition coils, not one). Is this just to power the ignition coils, or does it replace the points for timing or something?

Offline calj737

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #7 on: November 27, 2019, 05:56:49 pm »
Depending upon which mUnit you have, you either use IGN or AUX to power the coils AND the electronic ignition (if that’s what you have). There is no power supply required for points and condensers.
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Offline roach374

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #8 on: November 28, 2019, 10:12:19 am »
Here's mine, but I'm still trying to figure out where the clutch / neutral switches should connect, in order to prevent the starter from starting (ie: only start when the clutch is engaged). I'm also not sure about the wiring to the ignition...


Offline calj737

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #9 on: November 28, 2019, 01:55:57 pm »
You can't really use the CLUTCH and NEU Safety switch in conjunction with the mButton.

With the mButton, a double tap of the START button (LH switch) will KILL the motor (if you didn't know).
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Offline roach374

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #10 on: November 29, 2019, 10:43:09 am »
You can't really use the CLUTCH and NEU Safety switch in conjunction with the mButton.

With the mButton, a double tap of the START button (LH switch) will KILL the motor (if you didn't know).

Right, but is there some analog / electrical way to wire the clutch switch (to the solenoid or something) to prevent the starter motor from firing? I like this as a safety feature (inability to start the bike when clutch is out).

EDIT: hmmm. Looking at the CB500 wiring diagram, it seems like the bike doesn't even have a clutch switch. Maybe the whole thing is academic.
« Last Edit: November 29, 2019, 11:01:45 am by roach374 »

Offline calj737

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #11 on: November 29, 2019, 02:34:30 pm »
You can wire it through the solenoid, but it won't interrupt the mUnit signal from START. With your diagram and using the mButton, the START switch is going to activate the IGN port no matter what you do with a CLUTCH or NEU switch. This is one reason why I never use an mButton.

True, the 500 never had a safety switch, but 550s did.
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Offline roach374

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #12 on: November 29, 2019, 03:51:16 pm »
You can wire it through the solenoid, but it won't interrupt the mUnit signal from START. With your diagram and using the mButton, the START switch is going to activate the IGN port no matter what you do with a CLUTCH or NEU switch. This is one reason why I never use an mButton.

True, the 500 never had a safety switch, but 550s did.

Fair enough, but will it prevent the starter motor from turning?

Alternatively, I could wire the start button in series through the clutch switch, but that's a lot of wire and somewhat defeats the purpose of the mButton.

EDIT: That is, of course, if a clutch switch existed on the cb500, which it doesn't.

Offline calj737

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #13 on: November 30, 2019, 02:41:50 am »
Ignoring the mButton, you can wire the clutch lever switch inline to the solenoid, using the clutch switch as the "ground" for the solenoid. Power to it comes from IGN or AUX, but in order to transfer that power to the starter motor, the clutch switch would have to be pulled in. This in effect behaves as a NEU switch too, though it is NOT the same thing as the motor would start while in gear, but you'd have the clutch pulled, so as soon as you let go of the clutch the bike would move (if not also in NEU).

You can easily look at some later year 550 diagrams to see how the CLUTCH switch was wired to adapt yours if you ditch the mButton.
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Offline roach374

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Re: M-unit wiring diagrams for SOHC/4 bikes
« Reply #14 on: November 30, 2019, 08:29:24 am »
the motor would start while in gear, but you'd have the clutch pulled, so as soon as you let go of the clutch the bike would move (if not also in NEU).

This is basically exactly what I'm looking for. Cheers!

 

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