Topic: Wiring Honda CB900F '81 (SC01) with M-Unit

[quercus.dk]

Hi all

Thank you for letting me into this forum.

I'm rebuilding my Honda CB750F from 1982 (registered in 1984) with an 900F engine (SC01). I think this engine is from 1981?
I'm about to do a fully new rewiring with an M-Unit, new Reg/Rec from Rick's, an Antigravity 12 cell battery, etc.

I have watch a lot of video's on the Internet and search this forum for drawings on wiring and wanted to share what I have come up with, and hopefully give something back.

I do have some questions on 2 wires I can't seem to find out where to go and hope this forum can help. And please do feel free to add comments to my drawing!

• From the Alternator is 5 wires: 3 yellow, 1 black and 1 white.
  Where do the black and white go?
  
• The Denali Soundbomb comes with a wiring harness, with a relay so that stock horn can be used too. In my build I will not use stock horn and see no point in using the wiring harness. I simply would use a positive wire on the Output side from M-Unit to the Denali Soundbomb Horn and then ground it. On the Input side I use Revival Cycles push buttons. But Denali say that this horn draw a lot more current than a stock horn and therefore need this relay. Since I'm doing all new wiring, do I need this relay or is it just a matter of using e.g. 18 AWG og 12 AWG wiring cables?
  
  https://youtu.be/Jtoji9ckx8Y?t=99

Thank you in advance!

Best regards,
Henrik

[RAFster122s]

Henrik, welcome and sounds like a fun project. Calj737 is the Munit expert on the forum.
Your Munit horn output, what is it rated at? That will tell you if the Horn function needs to drive the relay or not. The Denali SoundBomb air horn is quite greedy with current, so you need to know if the Munit can handle the 30A load. It is going to dim your lights as 30 A draw is rather intense for our old bikes. What is the cb900 alternator output compared to the cb750?
David

[quercus.dk]

Hi David

Regarding the Denali Soundbomb I think I have figured it out
It has a current draw of 20 Amp, so i need a relay, since the M-Unit only gives 10A on Horn Output. I could maybe use the AUX2 with two wires, since this can give 20A.
I have updated my wiring diagram with a relay. I only have 1 question left regarding the Horn. From my understanding, everything from 5 from the Revival Cycles Starter Solonoid is behind the 30 AMP fuse? Therefore I can connect the relay 30 connector directly to the BAT pole on the M-unit?

Regarding the Alternator on 750 vs. 900, the Haynes Owners Workshop Manual wiring diagram is the same. Originally i bought this Honda as a 750 and putting a 900 engine on it was plug and play. Only add-on was clamps for the oil cooler on the 900cc.
And this was back in 1994 i did this engine upgrade So me and my old Honda goes way back

According to Haynes (and look on my bike) 5 wires going into the OEM Rec/Reg and 3 wires going out. But it does not tell why 5 wires in, becomes 3 wires out?
The 3 yellow is easy, they are just 1-to-1 from Alternator to Rec/Reg.
The 3 wires outs from Rec/Reg is:
Green goes to Ground
Red/White goes to Starter Solonoid (in my drawing this is the wire going to 6)
Black splits up, 1 going to Ignition Switch, 1 going to Kill Switch and Starter Switch (in my drawing this must be what I have on 3 from the Starter Solonid, going to Start on the M-Unit)

So the question is, do these two wires from the Alternator just go to positive and negative on the Rick's Rec/Reg?
White wire from Alternator goes to Rick's Rec/Reg Red/Positive connector?
Black wire from Alternator goes to Rick's Rec/Reg Black/Negative ground connector?

Sorry it bacame that long :-)

Best regards,
Henrik

[calj737]

The black wire from goes to the Regulator side of the Ricks. It is NOT a ground. It is the 12v sensing wire the regulator uses to determine the voltage requirements from the alternator. You can run that to the LOCK input on the mUnit. Once energized, that input will read the same voltage as the battery.

[scottly]

The DOHC charging system is different than the SOHC system. There were two black wires connecting to the stock reg/rect. One, that was grouped together with the red and green wires, is the switched positive 12V connection. The other black wire is the 12V output from the reg that connects to the black field coil wire in question. The white field coil should connect to the reg at the same terminal as with the stock harness.

[quercus.dk]

Hi

So the black wire from Alternator goes directly to Lock on M-Unit? And not like in OEM, in and out of Rec/Reg.
What about the white wire? Does it just vanishes?

I have attached my updated wire drawings.

Best regards,
Henrik

[calj737]

Wiring from the alternator goes to the Reg/Rec per stock. You can run a Black wire from the Reg to the Lock input for 12v sensing.