Regulator wiring help for use with Motogadget M-unit. Please Help.

Snickare

Snickare

Active Member
So, I've bought and wired a Motogadget m-unit into a custom wiring harness for my 1982 CB750. Here's my problem though. However good I am at researching and figuring out problems, this is eluding me. The black wire on the R/R goes to where?

I've gotten the bike to start up fine, and run fine, but it's obviously not charging the battery, as it has run down after several starts and will not start the bike any longer. I'm sure it's the black wire I need to do something with, but I'm not sure where to put it...
I need some help from someone that know electrical. Anyone able to offer some advice? I can provide a wire diagram if needed. or describe what I've done easily. It's really a pretty simple system to use.

Thanks
 
Ok, the black wire is often the ground wire if you are using an aftermarket R/R. What color are the other wires?

If it is the ground wire, it needs to be attached to the negative terminal on the battery, possibly through the frame, which should be grounded to the battery as well.
 
I have three wires coming out of my regulator. Red/white, Black, and Green.

The Red/White goes to my Starter Relay located on my Starter Solenoid.

The Green is Grounded.

The Black for now goes nowhere.....
 
I've done some experimenting. This is what I've found. Can anyone verify my work?

I'm sure there are not many people that are too familiar with the m-unit, but here goes-
I've tied my regulator to the lower two prongs of the starter solenoid. The red/white goes to the left prong the one that has continuity with the battery post of the solenoid. Then the black wire from the regulator I connected to the lower right prong in the starter relay.

My test; I started the bike, removed the positive battery cable, and the bike kept running. This means the bike is running off of the alternator/ regulator. When I tried it on my first attempt when the black wire went nowhere, the bike stopped running as the battery's positive cable was removed. This means as I was running it before, I was only running it off of the battery, hence my problem of draining the battery after several minutes.

My last concern, is that if the bike is running now off of the regulator/ alternator, when I removed the battery's positive cable, the lights started to dim until I twisted the throttle. could this mean my regulator is bad? Or is it just because of the lower idle? And the regulator only kicks in at higher RPM?

Any thoughts from any electricians out there?

Thanks
 
So this is not a stock R/R, correct?

That year of 750 uses an electromagnetic rotor spinning inside the stator for charging, so there has to be power going to the rotor. The stock R/R has hookups to provide regulated power to the rotor, so it might be easier for you to chase down a stock R/R to avoid having to rewire the whole charging system. They're also used on the CB900 of that year, so tracking down one shouldn't be too bad.
 
That's just it. My charging system IS stock. It's how it ties into the m-unit that makes the hook up tricky..
 
OK... back way up....

The M-Unit doesn't go anywhere near the charging system, so you want to retain stock wiring for the R/R.

All the wires from the R/R should plug into the alternator, with three exception: The red/white goes to your starter relay (solenoid). The green wire from the R/R should be grounded against the frame, plugged into another green wire on the harness, or go directly to the negative terminal on your battery (any of those three are acceptable). Finally, the black wire from the R/R should be plugged into the black wire from the harness (trace it back from the ignition switch if you're having trouble locating it and don't confuse this with the black wires coming from the rear turn signals).
 
Thanks, but as I stated, the wiring harness for the rest of the bike is based off of the new wiring for the m-unit. The black wire needs to close the circuit for charging the battery and running the ignition and accessories... But when you eliminate the rest of the harness where then should the black wire go...?

I did some testing and it seems that I may have found the right place for it. But does anyone have any concrete info for what the black wire needs to be tied into? I dropped it into the starter solenoid and then tested the running of the bike. With the bike running, I pulled the positive lead from the battery and the bike kept running. This should mean that the R/R is now in full circle, not to mention adding charge to the battery. Correct?
 
The black wire needs to go to a switched 12V source. When the ignition is turned on, black wire needs to have power. This is the signal wire for the regulator so it knows when to adjust the power running to the alternator (via the white wire).
 
Great. That should mean that by putting it on the relay for the starter, it's switched, and sending power.

Thank you. I'm trying it out now. Gonna run it around the neighborhood and see that it's making power and charging the battery.
 
I don't think the starter relay is a good place for that black wire. The starter relay only has power from the battery or from the starter button.

You want something that has power as soon as the ignition switch it turned on.
 
Actually... orange wire to the relay might work.

I'd still look for a spare black, though. That's where it's supposed to go...
 
Thank you for the input. But the suggestions have no correlation to the wiring of the m-unit... The starter relay is the only switched place for it to go to... there is no Orange wire, and there are no other black wires. Remember, it's a custom wire harness...
 
Snickare said:
Thank you for the input. But the suggestions have no correlation to the wiring of the m-unit... The starter relay is the only switched place for it to go to... there is no Orange wire, and there are no other black wires. Remember, it's a custom wire harness...
Click to expand...

I don't think we're talking about the same thing here.

Where is the starter relay getting power from?
 
The starter relay/solenoid gets power from the Battery.... The battery also goes straight to the m-unit and in turn sends a signal to the starter relay to 'start' the motor.
 
Exactly. So that's not a good source for the black. You're either stuck wiring it on the battery side so that it's on all the time or it's only getting momentary power when you're pressing the start button.

You need a source that's on when the key is switched on.
 
Here is a quick representation of my relay.

+B -M

Red I Green
-------------------
R/W I Black
(Fuse)

Red is from the start button on the m-unit. R/W is the Red/White from the Regulator/Rectifier. Green goes to ground. And the Black is the million dollar wire in question from the RR...

I checked the continuity between the Battery + and the location of the R/W. It showed that even with the motor off but key on, there was a loop. then i checked the same between where the Black is and the Battery -, there was also a good loop. Wouldn't this suggest that with the key on, and the motor running, that the RR is charging the battery and pushing power to the rest of the system? There is no continuity between the R/W location and the Black location on the Relay.

I've been all around my neighborhood today several times so far, and there have been no power failures. The battery sounds strong when starting the motor, and the bike is running very nicely. Is there any reason that I shouldn't leave it there?
 
All you need to do is find a wire that when the key is off reads 0 V to ground, and when the key is on the same wire reads 12.x V to ground. Then connect your black wire to that.

What sonreir is saying is that the starter relay is always 12 V, whether the key is on or off. Meaning that your alternator will always be pulling power for the electromagnet. Which probably wont drain the battery in a few hours, but let it sit for a week and youll come back to a dead bike.

And you do really nice (wood) work.
 
I need to double check that then. Thank you for the clarification. I'll go out now and look to see what those wires read.
Thanks for the kind words on my work too. I'll be posting pics of this very custom CB750 I just made on my blog. if you're interested please take a look.

Assuming this electrical issue is solved, I'm taking it in to get the carbs synced tomorrow. And then that should be the end of it... (knock on wood).
 
Re: Re: Regulator wiring help for use with Motogadget M-unit. Please Help.

SONICJK said:
And you do really nice (wood) work.
Click to expand...

Just followed that link - now very much looking forward to seeing this bike. You're a hell of a woodworker.
 
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