M-unit and Regulator/Rectifier for Honda CB 400 F

Hi guys!

I'm doing my very first build, and almost everything is new to me, so I naturally need a little help once in a while. It's a Honda CB 400 F from 77.

I have decided to go with a M-Unit V2 and also bought a combined regulator and rectifier. I'm currently drawing the new wire diagram, and I'm having trouble with the stator and R/R part.

Is this the correct way to connect everything? It's especially the black wire that I'm having doubt about.

Reg/rec is mostly correct. The black wire should go to the AUX output and not the ignition switch or LOCK. You should have a second red wire (fused) leading from the battery positive terminal, to the ignition switch. The black wire coming off the ignition switch should then go to LOCK.

Thank you for your reply. Can you explain why the black needs to go to aux output. I don't understand the function of the black wire.

The black wire on the R/R is dual purpose. It provides power to the unit so that it can energize the field coil, but also is the voltage sensing wire. The unit uses this power input to determine how much power to send to the field coil. When the system voltage is low, more power is sent to the field coil. This makes the electromagnet stronger and more electricity is generated by the alternator. When system voltage starts to get too high, less power is sent to the field coil.

The AUX output on the m-unit is sort of a generic output. It sends out 12V to anything that needs power that wasn't explicitly covered by any of the other outputs. Things like gauge lights, tail lights, the ignition system, and the regulator/rectifier fall under this category.

Thank you for your reply!