M Unit Blue Help CB750 1980

Racethepilot

New Member
Hey crew,

Trying again. I have wired the m unit blue and the bike will not start. When I hit the starter button the bike makes a spark noise then the m unit flashes and shuts off. I have attached how the bike is currently wired. Any help would be appreciated.
 

Attachments

Sonreir

Oregon
DTT SUPPORTER
The green/red wire in your diagram needs to be grounded.

Also, if you wired the solenoid yourself, be sure that then red/yellow wire does NOT have power when the bike is turned off. The red and red/white wires should have power when the bike is turned off.
 

SquidHunter

Active Member
Couldn’t you wire the m-unit independent from the solenoid? I’m not an electrical guru, but it seems like that would be easier


Sent from my iPhone using DO THE TON
 

Racethepilot

New Member
Red/ yellow has no power when bike is off. I have grounded the green red wire and still no luck. Any idea on the black wire?
 

Sonreir

Oregon
DTT SUPPORTER
Racethepilot said:
Red/ yellow has no power when bike is off. I have grounded the green red wire and still no luck. Any idea on the black wire?
Missed that one, sorry. That goes to the AUX output on the M-Unit. It will need power whenever the bike is turned on.
 

Racethepilot

New Member
Alright.

So wired the bike exactly like you said. Black to aux that gets power when bike is turned on. Green and red is grounded. When I hold the start button to cycle the starter the whole unit starts flashing and won’t stop flashing unless disconnected from the battery. Starter motor never makes a noise. Battery is fully charged.

Anything else I might have done wrong?
 

Sonreir

Oregon
DTT SUPPORTER
Grab a multimeter and disconnect the solenoid from the m-unit, but leave it connected to the battery. Check DC voltage on all four wires and report back.
 

SquidHunter

Active Member
One of the terminals on the solenoid is supposed to be a ground. That may be the green/red one there with the question mark


Sent from my iPhone using DO THE TON
 

Sonreir

Oregon
DTT SUPPORTER
SquidHunter said:
One of the terminals on the solenoid is supposed to be a ground. That may be the green/red one there with the question mark


Sent from my iPhone using DO THE TON
That's correct. Green/red should be ground. But by checking the wires with the meter we can be sure the wires are in their correct locations within the plastic connector.
 

Sonreir

Oregon
DTT SUPPORTER
OK. That's looking good.

Next step is measure resistance across the yellow/red and green/red wires.
 

Racethepilot

New Member
Idk what has happened. Now I have disconnected everything and when I try to simply turn the headlight on the whole unit starts flashing and won’t stop.
 

Sonreir

Oregon
DTT SUPPORTER
I can't recall off the top of my head, but the manual should give you a list of what all the different flashing means.
 

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