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Brake light help

Old 08-19-2010, 10:13 AM
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Angry Brake light help

Hello, I am trying to wire in a second set of brake lights for a little more visiblity. They are just basic led strip lights, should be easy. But the problem I have run into is that i have 6 volts between the green and green/yellow wires for the brake light without brakes applied. When I press either brake it jumps to full 12 volts. I have unplugged front and rear switches and also the blinker relay and still have 6 volts. I have searched most of the tail light mod threads and this does not seem normal. My bike is an '03 and I have done all of the work except for paint myself. I am fairly handy with a multimeter. But I am just missing something and have not been able to figure out what it is. Any help or ideas would be greatly appreciated.

Thanks, D.A.S.
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Old 08-19-2010, 11:19 AM
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Well i figured out the cause. It has something to do with the led bulbs that I have installed in the factory location. Maybe someone with a little more electrical know how can tell me why. With the key on, if I install regular old bulbs I have 0 volts between green and green/yellow with out brakes applied. When I apply brakes I get 12 volt like it should be. But when I install the led bulbs I am back to the orginal problem. Is this common to leds that are all lit at half brightness for marker and then move to full bright when brakes are applied?
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Old 08-19-2010, 11:24 AM
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Stixx, love the lower fairing, what brand ?
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Old 08-19-2010, 11:33 AM
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Thanks. Sharkskins. Both upper and lower farings.
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Old 08-19-2010, 01:12 PM
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LED are hooked up backwards thereby allowing voltage through?
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Old 08-19-2010, 06:37 PM
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No, They only light if voltage is applied in the correct direction. If wiring is reversed nothing lights up. thanks though.
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Old 08-19-2010, 07:27 PM
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Originally Posted by Stixx View Post
No, They only light if voltage is applied in the correct direction. If wiring is reversed nothing lights up. thanks though.
Then that means they are acting as diodes. Now you have to figure out where the voltage is coming from. You have a running light circuit to the bulbs which is on when the key is on and you have a brake light circuit which comes on when the brake is pressed. If you want them to be a running light AND a brake light you will have to hook up a diode to keep voltage from leaking over to the other circuit when you press the brake. If you only want to supplement your brake light, take the wire that goes to twelve volts as your HOT leg and hook that up in parallel to the + (positive) side of the LED. Take the other side of the LED to a good ground.
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Old 08-22-2010, 06:04 PM
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Hhhmmmm must have worked since no response.
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Old 08-22-2010, 07:43 PM
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Yes it is fixed. All that I had to do was swap out the led bulbs that came with the undertail for another set of 1157 leds. They look the same, light up the same. But it got rid of the 6 volts that was bleeding into the brake side of the circuit. Hell if I know why. The undertail came from france and there is no telling where the bulbs came from as they came with it. Been on to other projects with both bikes, added a comm system to ladys bike and little minor stuff that always seem to build up. Actually got some pics today of it in its current and maybe final stage. (yeah right) So if i get around to it in the next few days will post them for all to see. Thank you for the help.
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Old 08-22-2010, 08:53 PM
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If you want conspicuity put one of these flashers on. I have one on my 3rd brake light (on my givi top case) and it really gets your attention
http://cgi.ebay.com/ebaymotors/Smart...Q5fAccessories
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Old 08-22-2010, 09:26 PM
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Now that is a nifty doodad. Cool.
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