M.Unit Blue 1977 KZ650B

So I'm working on diagramming the wiring out before I order the Motogadget M.unit Blue. I don't have a lot of experience in wiring (shoot, I don't have a lot of experience in restoring a motorcycle either, but that hasn't stopped me from attempting to restore this one). Using the Clymer wiring diagram and the sample diagram from Revival Cycles I think I've got the wiring correct. Just wanted some other to take a look and see if I've missed anything.

I'm including the diagram I mocked up. 

At a quick glance it looks good.
The core concept with the M-unit is that everything goes to ground to complete the circuit (both the signal wires AND the power wires) including switches.  This can take a moment to wrap your mind around when compared to traditional motorcycle wiring.

For cross reference, here's my wiring diagram for my GS750:
(there may be a mistake in the diagram with the high/low beam switch that I fixed on the bike afterwards)

Also, you'll want to get a ferrule crimper and some bootlace ferrules... they ensure a good connection at the M-unit.

wrote:

Also, you'll want to get a ferrule crimper and some bootlace ferrules... they ensure a good connection at the M-unit.
 

Yeah, I picked up a ferrule crimper and some bootlace ferrules in preparation for the wiring job. 

When doing wiring below is a link to the tape you should use.  It sticks to itself rather than the wires, and this makes it great to use.  Also, it does not get gooey or otherwise deteriorate.  You stretch the piece you will use first, and this activates the adhesive; it only sticks to iteself.  I will never use anything else.  Ed

www.amazon.com/F4-Tape-Self-Fusing-Silic...a-325639701571&psc=1

650ed, thanks for that reply. I have a partially used rolls of that in my basement left over from my electrician days. Industrial jobs often called for that stuff for insulating large wire splices. In the trade it known as 'self-vulcanizing' tape. 

It's like magic. Every large splice gets a couple of layers down first. In the olden days we used varnished cambric, but what with modern technology...

Your diagram looks pretty good, but the battery isn't wired up properly. A smaller (11-13 gauge) wire should go from battery +ve to the main fuse and from there to the m-unit. Another 11-13 gauge wire should go from the reg/rec to battery +ve. Finally, a 6-7 gauge wire goes to the starter relay and from there to the starter.

Edit: looking at the m-unit instructions you need 9 gauge wire to the m-unit from battery +ve and a 40A fuse.

Varnished cambric??? That was BEFORE the "old days". 

wrote:

Your diagram looks pretty good, but the battery isn't wired up properly. A smaller (11-13 gauge) wire should go from battery +ve to the main fuse and from there to the m-unit. Another 11-13 gauge wire should go from the reg/rec to battery +ve. Finally, a 6-7 gauge wire goes to the starter relay and from there to the starter.

Edit: looking at the m-unit instructions you need 9 gauge wire to the m-unit from battery +ve and a 40A fuse.

So I based much of my wiring off the diagram that Revival Cycles has ( revivalcycles.com/blogs/technical-articl...-unit-wiring-diagram ), and according to their diagram with the integrated starter solenoid and main fuse they sell (which I'm planning to use) it's wired this way. Is this not correct?

Granted, I probably should have used smaller lines when designing my diagram which would have helped differentiate wire gauge. 

The wiring from the battery to the starter is OK, but should be at the bottom (on the solenoid and not the fuse). The other circuit goes from the reg/rec through the solenoid (should be rhe fuse) to the m-unit. If you swap them around then the starter circuit will be correct, but you'll only get power to the m-unit when the motor is running - makes it hard to start the bike I usually have a 13 gauge wire coming off the battery +ve with a double female bullet connector on it. Then I plug the rectifier into one side and in your case a fused wire to the mo-unit into the other.

Edited to add a diagram from the mo-unit instructions. I translated the parts (except "batterie", figured that one was obvious ). I would put the rectifier on the other side of the fuse (as explained above) to protect the mo-unit if there are any surges. 

Just looked at the revival cycles diagram and it is also wrong. Their alternative main fuse circuit is OK, but if you don't use that then there will be no power to the m-unit unless the bike is running.

Edit: So, I guess assumption is the mother of all... I took a closer look at the revival cycles diagram and it looks like they just labelled it in a confusing way. The label "Starter solenoid" and "main fuse" should probably just be combined and put underneath, the way they labelled it I assumed it was two seperate components just stuck together. Internally it seems that the battery positive is bridged to the fuse (blue circle below, this is missing in your diagram). This means that you can wire it up as you had planned. Sorry for any confusion, my mistake.