Topic: Quick question re:installing K3-K5 wiring harness in a K2

[Terry in Australia]

G'Day Guys, I'm close to finishing a K2 Cafe Racer build for Mike. In a moment of rare logic, I decided to buy a later wiring harness so that I could have multiple fuses as opposed to one fuse as per the standard K2 harness.

I started to install the harness yesterday and noticed that there's another multi-pin plug (red) that doesn't exist in the K2 harness, so I checked the parts manual for a K3-K4 and apparently that plug is for a "starter motor safety unit".

I've never seen one, (I don't think we had them on Aussie CB750's as we didn't get the K3-K5 here, we jumped straight from the K2 to K6) and so need to either find one and install it, or (my preference based on my ignorance of it's function) bypass it.

So my questions are as follows:

1. What's it for?
2. Do I need it?
3. Can I bypass it? and
4. If I can't bypass it, where can I get one?

Thanks in advance men, I won't touch it until I check your replies. Cheers, Terry.

[scottly]

G'day Terry.
1. It prevents the electric starter from operating unless the clutch lever is pulled in, the trans is in nuetral, or both.
2. Only if you accidentally hit the starter button with the bike in gear.
3. Yes, it can be bypassed.
4. A simple diode can be used to replace it, as was done on the K7/K8.

[SOHC4 Cafe Racer Fan]

One of those trade offs of safety versus taking more time to start from a first gear stall (as you need to switch back to neutral).

[scottly]

Terry, run a jumper from the green (ground) wire at the SMSU plug to the green/red wire in the plug.

[Terry in Australia]

Hey thanks Scott, looking at the diagram in the link, there are 5 wires going to the SMSU, do I need to jump any of the other ones? Cheers, Terry.

http://www.classiccycles.org/media//DIR_1205589/DIR_1277093/DIR_1296593/483c729cd55407e6ffff8793ffffe41e.pdf

[edwardmorris]

I'm sure I have one laying around if you need one Terry, but please post here if you manage to bypass it altogether.

[70CB750]

I done it to F harness, very easy.  Connect one post on the starter relay to battery (+).  The wire from the other post goes to the  Start button on the  right hand control and when you push it, it grounds it and completes the circuit.  Thats all you need.

[scottly]

Hey thanks Scott, looking at the diagram in the link, there are 5 wires going to the SMSU, do I need to jump any of the other ones? Cheers, Terry.

http://www.classiccycles.org/media//DIR_1205589/DIR_1277093/DIR_1296593/483c729cd55407e6ffff8793ffffe41e.pdf

Hey Terry, there are a couple of errors in that diagram. I was working from the same one a few years ago, helping Jim F, when I noticed them.
In your case, it might be easiest to do the bypass in the headlight bucket: connect the solid green from the start switch to one of the green wires on the new harness, and connect the yellow/red wire from the start switch to the yellow/red wire on the new harness. The SMSU plug will be unused.
For those that have a clutch switch, the SMSU can be replaced by inserting a diode between the green/red and light green/red wires at the SMSU plug, with the cathode connected to the light green wire. The diode should be rated for over 4 amps.

[Terry in Australia]

Thanks Scott!

[Riceman]

Yeah thanks Guys,This will save me some headaches also.

[scottly]

Terry, there will be a green/red wire in the new harness that will also go unused, just in case you got to wondering about it.

[70CB750]

I done it to F harness, very easy.  Connect one post on the starter relay to battery (+).  The wire from the other post goes to the  Start button on the  right hand control and when you push it, it grounds it and completes the circuit.  Thats all you need.

Correction: posts are for the high amper circuits, my bad. I used those other two wires of course, one for + and the other to ground via Start switch.



Does not hurt to try the relay first if it indeed works.