Topic: Backwards Engine Cutoff Switch

[Rhonda_the_honda]

Hello! I am VERY green to engine rebuilds, but decided to take on a '78 CB750K as my first project. I've rewired the bike, but am having issues with the right-hand switch wiring.

This video helped a TON, thanks to Taylor (Classic Octane) I was able to follow along and rewire her myself.    https://youtu.be/NK0s6AHycdk

This is the switch I bought: https://4into1.com/reproduction-throttle-switch-assembly-35130-404-671-honda-cb360-cb500-cb550-cb750/

I'm using an Mo.Unit Blue to replace the original wire harness.

In Classic Octane's video, Taylor shows only ONE sold black wire on his OEM switch. Mine has TWO solid black wires. I tested each with the voltage meter and only one showed continuity. I currently have that wire connected to INGNITION OUT on the Mo.Unit, and the opposite wire connected to KILL. This makes the engine cutoff switch backwards - but atleast it's functional.

When I connect both wires to eachother the engine cutoff switch doesn't work - it starts regardless of where the switch is. When I swapped the wires, nothing happens.

What else should I try? I really hope someone here can point me in the right direction.

[Rhonda_the_honda]

The switch assembly you have should provide continuity across both black wires while the KILL button is depressed.

The mo.unit works opposite of the stock switch because it looks for ground.. correct? If so, it makes sense that my switch is backwards, b/c the switch is grounded in the OFF position and continuous in the "RUN" positions. How do I get around this with there being two black wires? I saw someone mention a reverse relay, should I look into this?

Using a voltage meter I clipped the ground to the b/w wire and the red/live to each black wire. I remember only 1 of the black wires showing continuity when the switch was in the center position. (29:00 on Classic Octane's vid https://youtu.be/NK0s6AHycdk)

My memory has been proven wrong before, so I may retest this after work today.

[jpdevol]

The aftermarket (and OEM) RH switch share a common “hot” input – black wire – between the kill (coil +) and the starter function. Additionally, the starter button completes the headlight circuit when off (out) and opens that circuit when button is pushed.

So, to separate the “kill” function from the starter function, the black circuit will have to be separated within the switch assy. One black wire can then be connected to the M-Unit output “Ignition”, then the black/white wire would continue to both coils (+) as normal.

A second wire to the remaining “black” side of the switch’s starter button can – 14awg size – then connect to M-unit output “Start”. The Switch’s Yellow/red wire should be 14awg and connect to start solenoid (+).

The Black/red switch wire can be dispensed with and the headlight circuit powered directly through another switched circuit or programmed via M-Unit functions to off until dimmer (hi/lo) switched is activated.

M-Units can be easier to wire from scratch with momentary switch inputs, but are harder to wire via OEM systems.

[Don R]

 The stock kill button in the run position provides a contact from 12V+ black wire to the black/white wire that feeds the coils.  In kill position that switch is open.

[jpdevol]

The stock kill button in the run position provides a contact from 12V+ black wire to the black/white wire that feeds the coils.  In kill position that switch is open.

Yep

[Rhonda_the_honda]

Thanks all, I tried what jpdovel suggested, connecting the "other" black wire to START-OUT, However it didn't work. I'm afraid my green background made this much harder than it should be.

In a previous post someone mentioned they made a negative triggered relay to keep the original function of the OEM/Aftermarket engine cutoff switch. I did this, and it's working as it should.

Here's the YT video I used to help explain how to make a negative triggered relay (I used a 4 prong relay).

Dropped the YT vid above incase anyone else has the same problem. I'll come back in a bit and explain what wires connected where.