Hey all!

I have a 2016 Street Twin that I recently had some work done at a dealership and a third party. Dealership worked on my transmission as I dropped it and bent something ion the detent arm assembly. The third party work on my tires, chain, and brakes.

Finally got it back after 2.5 months of waiting for repairs to be completed only to have found ANOTHER issue. Upon acceleration, my bike would randomly loose power. After some online research, i found that the brake switch is my issue and I confirmed this in my own findings. My brake light never dims, it only stays on at the brightest as if Im braking.

Thinking it's a simple adjustment to the rear brake and how it triggers the brake, I started my work. HOWEVER, when i removed the brake switch to test it, it still didnt stop the brake light from being activated.

As it turns out, when I press BOTH brake switches, the light will dim! If only one switch is pressed, the light will remain bright. This suggests to me that the polarity of the switch has been changed!

How do i change back the polarity because I cant figure it out. ECU restart didnt do anything and I cant find any information about a relay. Any help will be greatly appreciated!

The "polarity" of the brake switch doesn't appear to be the issue and likely the plug can only be connected one way. If you disconnect both brake switches what happens? I think that the problem lies elsewhere. Check the connections of the brake light where it joins to the main harness at the mudguard, perhaps the connections have been reversed somehow. As to the loss of power, I don't see why the brake light would cause it at all.

 

That's what doesnt really make sense to me either with the polarity being the issue. But it's odd that a switch would have this kind of issue.

If you disconnect both brake switches, what happens?
I haven't been able to figure out how to disconnect the front brake switch from the main harness but I'll look under the mud guard as you specified to see what happens. I'll keep you posted once I complete this task.

As for the power, I read on another forum that with current bikes, the ECU will cut some power to the engine if it senses the brakes have been applied. It was never a complete power loss but a "hey, you have you are applying brakes while at full throttle. I'm confused so I'm taking some power away from you."

 

IIRC, the rear brake switch only gets continuity thru the front brake switch (to accommodate a criuse control) whenever the front brake lever is released. If you don't have CC, get rid of that tiny front micro switch and crimp on a couple 90⁰ female spade connectors with black and blue in one, red in the other and use a standard sized switch. Mine failed years ago so I replaced it with Honda 35340-MM5-600.

 

And modified for use with the common front brake switch found on most bikes.

 

Thanks Nigel! However, I dont think just a new switch is the issue. Something else is going on that I cannot figure out at all.

 

The plot thickens.

Ordered a new rear brake switch connected it and the problem was NOT rectified. Even checked by replacing the old switch and putting the new switch on the front which resulted in no change to the problem.

Here are the combinations I have tried and the results:

• Rear Brake Switch (RBS) NOT pressed + Front Brake Switch (FBS) NOT pressed = LIGHT ON
• RBS pressed + FBS NOT pressed = LIGHT ON
• RBS NOT pressed + FBS pressed = LIGHT ON
• RBS pressed + FBS pressed = LIGHT OFF
• RBS disconnected + FBS connected and NOT pressed = LIGHT ON
• RBS disconnected + FBS connected and pressed = LIGHT OFF
• RBS connected and NOT pressed + FBC disconnected = LIGHT OFF
• RBS connected and pressed + FBS disconnected = LIGHT OFF

ALL TESTS WERE DONE AFTER THE ECU HAS BEEN DISCONNECTED FOR 4 DAYS

It is clear to me now that the switch is NOT the issue but something else is entirely. I found it interesting that the front switch, when disconnected, dimmed the light but the rear still didnt turn on the light when pressed.

I doubt that a new FBS would do anything because i connected my NEW switch to the connector and found no change in results, pressed or unpressed.

 

• Rear Brake Switch (RBS) NOT pressed + Front Brake Switch (FBS) NOT pressed = LIGHT ON
• RBS pressed + FBS NOT pressed = LIGHT ON
• RBS NOT pressed + FBS pressed = LIGHT ON
• RBS pressed + FBS pressed = LIGHT OFF
• RBS disconnected + FBS connected and NOT pressed = LIGHT ON
• RBS disconnected + FBS connected and pressed = LIGHT OFF
• RBS connected and NOT pressed + FBC disconnected = LIGHT OFF
• RBS connected and pressed + FBS disconnected = LIGHT OFF

If you are pressing the button on the switch (not the lever or pedal) then everything in that list is working correctly. Button out is what makes the light come on, not button in. In other words, applying the brakes lets the button out and releasing the brakes pushes the button in so it might seem counterintuitive.

Is the nub on the front brake switch housing missing or damaged resulting in the switch not getting depressed when the lever is released? Can hear the switch click when you pull in the lever? Stock brake lever?