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nyc_gs 11-09-2007 09:33 PM

640 Adventure rear brake light switch
Upon attempting to get my updated NY State inspection sticker, it was brought to my attention that my rear brake pedal is no longer activating my rear brake light.

So, thinking this should be simple, I decided to poke around today.

I examined everything I have hi-lighted in the image above and found nothing out of the ordinary. Fuses are also all ok.

The one question I have is this: the line that runs from the switch up to the wiring harness, where exactly does that go? It seems to run forward under the tank, but then I lose it. (Did not remove the tank.)

I checked what I think is that switch where it connects with everything else near the battery but all connections seem fine.

The brake light functions perfectly fine when the front brakes are used, just not the back brake.

Anyone have any suggestions where I should be looking here?


-- Jason

Luke 11-10-2007 12:02 AM

First off, clean the connector and check the wiring on the switch pigtail. It's exposed, and might get damaged.

Got a multimeter?
Unhook the switch from the wiring harness and measure it's resistance. It should be high (more than 10K ohms) when the brake is off, low (less than 2 ohms) when it's on. You may need a fair bit of brake pressure to turn the switch on.

No multimeter?
Unhook the switch from the wiring harness. Turn the ignition on. Short circuit the two pins in the wiring harness connector to each other with a bent paperclip or something. The brake light should light. If so, the problem is not the harness.

Now you know if the problem is in your switch or the wiring harness.

Bad switch? Check the pigtail again, then try a new switch.

Bad harness? Now you really want a multimeter. Turn on the ignition. Measure the following voltages relative to battery ground:
Yellow/blue wire at connector +9V or more is good
Green/white wire at connector, front brake off +2V or less is good
Green/White wire at connector, front brake on +9V or more is good

Turn off the ignition, and measure the resistance from the green/white wire at the connector to battery ground. Less than 6 ohms is good.

Kaineb 11-10-2007 02:29 AM

These switches take allot of punishment and need to be replaced after a bit. Mine did the same. It's not expensive. Buy the #30 and 31's. Simple install and bleed your back brake. Make sure you torque it properly.

FYI, front brakes obvioulsly have a circuit of their own that activate the back brake. After the simple swapout, it will work like a charm.

nyc_gs 11-10-2007 05:47 AM

Ok, thanks guys.

Where exactly does that wire run? (#31 in the diagram)

It seems to run forward under the tank, but I assume it turns and heads back and ends near the fuse box along with everything else, yeah?

I was expecting that to be a fairly short wire, but it seems a bit excessively long.

Thanks again for the input, appreciated.

-- Jason

Luke 11-10-2007 12:48 PM


Originally Posted by nyc_gs
Where exactly does that wire run? (#31 in the diagram)

On the '02s, it runs under the tank and connects there. It's probably the same on the later bikes.

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