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Discussion Starter #1
Hello,

Just purchased a 2003 RC51 and I'm having some issues. When I purchased the bike the only issue with the bike was that the brake lights were always on. After looking into it, it looks like the previous owner unplugged the front brake switch from the front brake. Unfortunately, when I press the button for the switch, I hear a click and the power for the bike turns off (instrument cluster goes out/brake light turns off). The bike has quite a few aftermarket modifications and the wiring on it in the rear is a joke. I've already removed some led's that were on the swingarm and in the radiator vents. The bike has an aftermarket undertail kit and the wiring looks like a Christmas tree.

I'm hoping I haven't bit off more than I can chew. I'm planning to get a different undertail kit and wiring everything back to stock so that I can figure out what is what.

Let me know if you have any ideas.
 

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Gd luck on the wiring dude...hope u ride her sooner
 

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I had to replace all my wiring harnesses due to the butchery from the previous owner.
When I first lifted the rear cowl panel and peered inside, I almost fainted at the hack job he did on the rear fender to fit the undertail.
I think he used a chain saw to trim the rear fender, and did such a bad job he had to use zip ties to hold it up.
The wiring "mess" as a result was pure chaos with relays bouncing loosely inside, and it had wires that had exposed ends begging to short out somewhere.
I managed to patch it enough to work, but eventually ripped it all out and redid everything from scratch.
Now it's all nice and well organized.
 

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Discussion Starter #5
Thanks guys, so do you think its just a short somewhere in the wiring that is causing the bike to turn off when I use the front brake?

I was planning on purchasing a new undertail kit and wiring it up to the factory wires (the current undertail kit has a separate box that uses a mess of wires). On my last RC51 I had the 'texas tuck', anyone know if anyone sells that undertail anymore? I could only find 2 different undertail kits when I searched.
 

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You stated that the previous owner had unplugged the brake switch, and that when you press the switch you loose all the instrument lights after hearing a click, soo I'm assuming that you plugged the switch back?
If that's the case then i would first of all unplug the wires from the switch again, then check the fuses and see if any of them blew, after wards you would need to do a resistance check to ground on the switch, that way you can determine if its the switch or not, then move on from there.
This is my first v twin sport bike, but it seems that between the motors vibration and ignorance from previous owners, there's quite a bit of electrical gremlins with these bikes, Good luck and keep us posted on your progress.
 

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Discussion Starter #7 (Edited)
Thanks larry, Haven't hooked the switch back up to the front brake lever b/c I need to order the screw to screw it back in. So I've been pushing the button down to check it.

I'll check the fuses again tonight, but I don't think its a blown fuse. When I release the button for the switch all the lights come back on. But whenever I push the button down again all the lights go out. The previous owner just rode around with the switch unplugged b/c the bike runs fine as long as the button isn't getting pushed, lol. Well it runs fine except that there is always the worry of getting run over for not having working taillights.....
 

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If I understand, with the front brake light switch connected (although not installed), if you activate the switch you lose all lighting and the engine cuts out, but if you release the switch, everything comes back on (excepting the engine which has died)? Except the brake lights stay on.
Well off hand it can't be fuse since it would stay blown.
And there are no circuit breakers, so it got to some relay mis-wired somewhere.
Let me check over the wiring diagram for a clue.
 

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Discussion Starter #10
2 Wires are going to the front brake switch: Green w/ yellow stripe and White w/ green stripe.

When i press the button on the switch, everything on the bike shuts off, including the tailights. Haven't tried it with the motor running, but I would guess the motor would turn off as the odometer display resets and goes into its start up mode as soon as I let go of the button.

I've only tested it with the key in the on position and the motor off.
 

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Discussion Starter #11 (Edited)
*** Update ***

Just checked Fuse D (White/Green) and the fuse was blown (almost looked half blown). Replaced the fuse and brake light is still constantly in the on position. However, when I press the front brake switch button, everything stays on (woohoo!), and the brake lights disengage (light is still on, but shows no brakes are being applied). I'm guessing this switch is a backward switch, so once my screw comes in to install the switch back to the handle, I should be able to ride.

Wished I knew why the fuse half blew though....
 

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Glad to hear

Great to hear that you found the blown fuse, but I would also be concerned with the cause of the blown fuse, maybe Sub Sailor can find where those wires run to and from, that way you can take a closer look at that specific part of the harness, good luck my friend. :)
 

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The wire color code he reported does match the ones for the front brake switch.
The Fuse D is for turn signals, front/rear brake lights, and horn.
Fuses don't blow without a reason, and with all the wiring done for the LEDs everywhere, it should be entertaining localizing the problem.

I'm surprised by bike didn't have electrical problems when I bought it.

Here's what greeted my eyes when I first got the bike:
Note the exposed green wire near the relay...sweet.
And all the relays and Power Commander were just bouncing around.


After replacing the wiring harnesses and a bunch of other stuff, it now looks like this:


So it might take some work, but don't give up on her yet.
Actually, working on them can be fun.
 

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Discussion Starter #14
Thanks for the help! My hope is that the LED's were causing the short (part of them were broken), and now that they have been removed the bike should be ok.

I'd like to replace the undertail and wire everything from scratch. However, I've only seen two undertail kits. Is there a website that shows at the different types for the RC?
 

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Mine looks twice as bad as that only because the stupid undertail I have the wire colors didn't match the stock colors so it looks funny. It all works though so I'll go with it.
 
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