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Author Topic: Motogadget M-Unit Blue, Rick's Regulator/Rectifier and ignition switch  (Read 926 times)

Offline Deuterostomia

  • Posts: 14
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

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Offline Sonreir

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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.
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Offline Deuterostomia

  • Posts: 14
http://forums.sohc4.net/index.php/topic,159934.0.html

I actually came across the thread you linked, but wasn't sure if the wiring held true for a dohc CB750.

-Drew

Offline Deuterostomia

  • Posts: 14
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


Offline Sonreir

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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.
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Audaces fortuna iuvat.

1977 Honda CJ360 - Café SOS - Stage One™, Café SOS - Stage Two™
1976 Puch Maxi - APuchalypse Now
Suzi T500 Cobra Resto

Custom Gauge Graphics
Custom Wiring Harnesses

DTT Red, White, and/or Black 360 Club - Better than those Blue guys

Offline Deuterostomia

  • Posts: 14
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

Offline Sonreir

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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.
Sparck Moto - http://www.sparckmoto.com

Audaces fortuna iuvat.

1977 Honda CJ360 - Café SOS - Stage One™, Café SOS - Stage Two™
1976 Puch Maxi - APuchalypse Now
Suzi T500 Cobra Resto

Custom Gauge Graphics
Custom Wiring Harnesses

DTT Red, White, and/or Black 360 Club - Better than those Blue guys

Offline Deuterostomia

  • Posts: 14
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