Motogadget M-Unit Blue, Rick's Regulator/Rectifier and ignition switch

Deuterostomia

New Member
Hey everyone, my name is Drew and I am new to the forum as well as this hobby turned obsession. That said, I suppose a little background information on my ride will be required. I purchased a stock 1981 CB750F that I am slowly turning into a brat/cafe racer mongrel. Anyways, I have come across a problem, or two that requires some expertise before i go any further with my build. That said, heres my initial question

1. Wiring the ignition switch to the m-unit or splicing it into the ignition/charging harness:

Using the factory schematic i believe that the only wires that i need to utilize are the black (ignition) and red (bat1) wires. Black runs to the regulator/rectifier and red to the starter relay. That being said, do i need to splice these wires into the ignition/charging system at there respective locations, or do i hook them up straight to the m-unit? If they hook to the m-unit, which input or output do they go to?

Thanks,

Drew
 
Deuterostomia said:
Hey everyone, my name is Drew and I am new to the forum as well as this hobby turned obsession. That said, I suppose a little background information on my ride will be required. I purchased a stock 1981 CB750F that I am slowly turning into a brat/cafe racer mongrel. Anyways, I have come across a problem, or two that requires some expertise before i go any further with my build. That said, heres my initial question

1. Wiring the ignition switch to the m-unit or splicing it into the ignition/charging harness:

Using the factory schematic i believe that the only wires that i need to utilize are the black (ignition) and red (bat1) wires. Black runs to the regulator/rectifier and red to the starter relay. That being said, do i need to splice these wires into the ignition/charging system at there respective locations, or do i hook them up straight to the m-unit? If they hook to the m-unit, which input or output do they go to?

Thanks,

Drew

For the ignition switch, the red wire should run from the m-unit's connection to the battery, through a fuse, then to the ignition switch. The black output wire from the ignition switch then goes directly to the LOCK input side of the m-unit. All other black, brown, and brown/white wires on the bike (if still needed, such as the regulator, power to the kill switch, gauge lights, tail light, etc) should connect into the AUX output side of the m-unit.
 
Sonreir™ said:
For the ignition switch, the red wire should run from the m-unit's connection to the battery, through a fuse, then to the ignition switch. The black output wire from the ignition switch then goes directly to the LOCK input side of the m-unit. All other black, brown, and brown/white wires on the bike (if still needed, such as the regulator, power to the kill switch, gauge lights, tail light, etc) should connect into the AUX output side of the m-unit.

I ended up figuring out the issue on my own by removing the ignition switch and metering for continuity between the Red and Black wires. When the switch is in the off position there is no continuity and when it is in the on position there is. I also came across a simplified schematic on the sohc forums. If the wiring is essential the same, which it looks to be, can I go just go by it?

Also, in the schematic, which i have attached, there is a black wire from the regulator/rectifier that is spliced into the black wire from the ignition switch. It then also goes to the lock input of the m-unit. That said, my next question is what purpose does it serve? I read that it is a sensing wire, but what does it sense?

-Drew
 

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That's more or less correct, but your wiring for your ignition system will be different. You should have two spark units on your bike. Each will need to get power, go to their respective ignition coils, and also connect to the pickups inside the engine.

I would also add a fuse between the battery and the ignition switch. A ground wire should also exist between the battery and the frame and possibly a redundant wire directly to the m-unit as well.

The black wire on the R/R is the voltage sensing wire and the power wire for the R/R. It's used by the R/R to know when to start regulating the field coil as well as providing a power source for the field coil. On your bike, there will be two black wires, but no green wire. One of the black wires should go to the AUX output (not the ignition switch) and the other will go to the alternator. Going directly from the ignition switch to the R/R bypasses the internal circuit breakers on the m-unit: not a good idea.
 
Sonreir™ said:
That's more or less correct, but your wiring for your ignition system will be different. You should have two spark units on your bike. Each will need to get power, go to their respective ignition coils, and also connect to the pickups inside the engine.

I would also add a fuse between the battery and the ignition switch. A ground wire should also exist between the battery and the frame and possibly a redundant wire directly to the m-unit as well.

The black wire on the R/R is the voltage sensing wire and the power wire for the R/R. It's used by the R/R to know when to start regulating the field coil as well as providing a power source for the field coil. On your bike, there will be two black wires, but no green wire. One of the black wires should go to the AUX output (not the ignition switch) and the other will go to the alternator. Going directly from the ignition switch to the R/R bypasses the internal circuit breakers on the m-unit: not a good idea.

If I am utilizing the original harness for the alternator, starter, spark units and ignition coils, do i need to provide a power wire to the spark units and coils or do they draw power directly through the original harness?

Also, on the regulator/rectifier, which black wire do i need to splice into and run to my keyed ignition switch? Is it the black wire in the 5 pin connector or is it the black wire in the 3 pin connector.

Thanks,

Drew
 
The spark units and the coils will both need power, preferably fed from the AUX port on the m-unit. For the regulator/rectifier, the black wire that's in the four pin connector along with the red and green wires is the one you'll want to use. The other black wire should connect to the alternator.
 
Couple more questions and then I believe I will be set.

1. The motogadget schematic shows that the start wires that come from the output side of the m-unit are spliced together and then one single wire connects to the starter solenoid. My question is where does the wire connect on the solenoid? Does it connect to one of the terminals, battery or motor, or does it connect to a wire in the connector.

2. Concerning power supplied to the spark units and the ignition coils, I understand that they should be powered by the aux output, but am unsure of where to splice power into the units themselves. That said, do i splice into the black/white wires that connect the two spark units and ignition coils together? The black/white wires are the wires that ares spliced together from the factory, and connect both spark units and ignition coils to each other.

Thanks,

Drew
 
1.) The solenoid for most of the DOHC bikes has a four pin plug. One is ground, one is to activate the solenoid, and the other two are always on. Skip these last two, no longer needed. The green/red wire can be grounded. The last wire, yellow/red goes to the output for the start on the m-unit.

2.) Doesn't really matter too much so long as the output from the kill switch goes to the coils. Leaving the spark units with power when the coils are off won't hurt anything.
 
Rick Reg/Rec only utilizes three of the four pins in the connector that plugs into the solenoid. The colors are red/white, black and green. However, I do see a red/yellow wire in the schematic that runs from the solenoid to the start button. That said, do i utilize that spare pin slot, and if so do i simply run a wire from the start output of the m-unit to it?

Thanks,

Drew
 
Deuterostomia said:
Rick Reg/Rec only utilizes three of the four pins in the connector that plugs into the solenoid. The colors are red/white, black and green. However, I do see a red/yellow wire in the schematic that runs from the solenoid to the start button. That said, do i utilize that spare pin slot, and if so do i simply run a wire from the start output of the m-unit to it?

Thanks,

Drew

Scratch that, I misread the schematic. Which makes way more sense now.

Thanks,

Drew
 
Got everything hooked up today, but wanted to test each circuit before I finalized the wiring and harness. Connected power to the m-unit, this was the first time doing so, and nothing happens. The leds do not go through there initial startup sequence and none of them come on. The only led that illuminates is the Bluetooth led which blinks a steady amber color for approximately 10 seconds before turning off. That being said, does anyone know what the blinking amber led means?

Thanks,

Drew
 
It will hopefully say in the instructions. And I wouldn't expect the LEDs to turn on until the power for the bike is on (either through the Bluetooth signal or the standard means).
 
Good news and bad news. I'll start with the good first. Got the m-unit installed and figured out that the blinking of the bluetooth LED is normal and is indicative of the m-unit getting 12v from the battery. As you (Sonreir) stated previously, the m-unit does not go through its startup sequence until 12v is provided to the "lock" input. After that the m-unit goes through its initial diagnostics.

Now for the bad news, well not really bad, just not good in regards to progress being made on getting this bike started. That being said, when I power everything up I keep blowing a 30a fuse. I was able to isolate the two parts of the electrical system, M-unit and ignition system by removing one fuse at a time and then powering everything up. What I found was that the ignition side of things is where the fault lies. I then checked all of the wiring and found that I have a short to ground at the plug side of the starter solenoid. I then proceeded to check all of my work making sure that I followed your (Sonreir) directions. What I found was that the green/red that I had previously grounded to my electronics box was the culprit. When it is grounded to the electronics box it will cause a one of my two fuses to blow. All that being said, my question is what does this wire go to? It is obviously a power wire, but what does it power? Where does it connect to the m-unit?

Thanks,

Drew
 
Dark green and red is usually for the ground side of the solenoid. It can also be used for clutch safety switch.

Where is the wire coming from?
 
From the starter solenoid to the reg/rec, the ignition side is wired as follows.

Red/white solenoid to red/white reg/rec
Red solenoid was dispensed with as it originally would have run to the keyed ignition switch
Red/yellow solenoid to start output of m-unit
Red/green from solenoid to ground (wire that when grounded turns into a mini arc welder) :eek:

Also, from the reg/rec I have the black wire running to aux output of the m-unit and the green wire running to ground.

The factory schematic shows that red/green should indeed run to the clutch safety switch. I wonder if maybe I had the connector installed 180 degrees out, though this seems unlikely given its more difficult to seat that way. As for the solenoid, how do i know which pins are the ground side and which are the power side?

Thanks,

Drew
 
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