Topic: CB550 K0 bike starts when brake lever is pulled

[extrafunky]

I'm usually pretty good with wiring but this one has me stumped. Happens intermittently. When ignition is on, turning the light switch (RH) on or pulling the brake lever triggers the starter solenoid!

Repro switches and main harness installed last year. I ruled out the RH switch since the brake lever is not part of that circuit, and all the switches checked out OK. I thought it could be grounding issue in the main harness or inside the headlight bucket but the solenoid is also sticking sometimes when this happens so I thought maybe it's a faulty solenoid. Sticking solenoid could be a different issue but needs to be replaced anyway so I got a new one and see what happens.

Anyone has thought on what might be causing this? 74 CB550K.

[Kenzo1979]

Wow!  That’s a good one.  Well, I would look at the hydraulic switch on your front brake and see if it is somehow wired to your electric starter button.  I honestly don’t see how that is even possible.  Can’t wait to hear the ending to this one.

[Gurp]

The fact that it only does it intermittently says that it's likely to be a loose connection that they share or more than likely is a spot where your insulation has rubbed through on your control wire for your solenoid and your brake.

Just my 2cents. I have to trace down issues like this more often than I care to on machines at work.

Hopefully you find it but it's going to be a headache to find.

My first guess on attempting to find this would be find a loom that they share or a plug wiggle the wire around in various ways and look for continuity between the pins.

I wish you the best of luck on what is going to be a challenging issue

Sent from my LE2127 using Tapatalk

[extrafunky]

Yeah, I also believe it's more likely a connection rubbing inside the headlight bucket but it doesn't really make sense.

If the brake switch triggers the starter solenoid, you would think the starter button would turn on the brake light but no, it doesn't do that. It just turns on the solenoid.

Also, when the brake triggers the solenoid, the brake light doesn't turn on just like when the running light switch triggers the solenoid, the lights don't turn on.

It's working right now but I still replaced the solenoid because of the sticking issue. Starter motor running continuously at 1am was not fun and realizing pulling out all the fuses does nothing.

[TwoTired]

Could be a faulty starter safety unit. Intermittents can be a #$%* to isolate. 
The safety unit is looking for either the clutch pulled in or the trans neutral switch while the starter button is pushed.
You could check those inputs to the unit to see if the conditions are met to activate the solenoid while the fault is present.  Your clutch switch is probably ok.  But perhaps your starter button is faulty or the wires going to it are grounding out.

Suggest you see if the turning the bars can make the intermittent failure solid.  If so, its likely a chaffed wire.

[RAFster122s]

Bad grounds can cause all sorts of odd behavior on some cars ai have owned in the past. Don't rule out it is making an alternate path to ground causing the odd behavior. Clutch switch wiring issue possibly...
Never a bad thing to clean and new dielectric grease on ground points as a start.

[Kenzo1979]

I think I know the issue.  It’s not the brake lever, it’s under the RH control housing.  It’s not a “bad” ground, but most likely an accidental ground.  In the 550, Yellow/Red is linked to Green/Red when the starter button is pressed.  Green/Red then has to pass Yellow/Red through the Starter Safety circuits in order to activate the electric start, but Ultimately it is giving your Starter Solenoid a ground to the already established Ignition Positive (Black + wire) to trip the magnet and turn the starter motor.  Bottom line:  your Yellow/Red is simply touching your bare handle bar which is grounding and completing the starter circuit, bypassing the SSM Unit (starter safety module).  Open your controls and make sure Yellow/Red is not cutting through it’s wire jacket at the handlebar internal wire route entry OR simply touching the top of the bars where it is soldered inside the control housing.  Pulling the brake is coincidentally just adding enough pressure to make this connection touch.

[zabzob]

Nobody wants to say it, so I will.

Your bike is haunted as ****. You don't need a mechanic, you need a priest.

[Gurp]

Nobody wants to say it, so I will.

Your bike is haunted as ****. You don't need a mechanic, you need a priest.

Sent from my LE2127 using Tapatalk

[extrafunky]

I'd say it was a faulty starter solenoid. Never had the issue since replacing it. Thanks all.