Brake light wiring Question 1978 XS 650se

Superdriver

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There are 3 wires on the harness that go to the brake light. They are Blue Yellow and Black. This matches up with the schematic . The Black is obviously for ground but I am not sure which of the others is the main power wire and the one that works off the lever to get the light to go bright. I get lost when I try to trace the schematic back LOL. I have just installed a Quick Disconnect Block for the rear wiring so I can remove the fiberglass seat and rear wiring for ease of other maintenance.. The LED brake light has a Black, Red and Grey Wire. Every thing works except that The brake light does not go bright all the time when activated. This seems to happen After I move the seat assembly around a bit. I really took my time matching up all the wires going into and out of the block. There is power to the tail light as it lights up when the key is turned on and the turn signals work fine. The only problem is the brake light not activating all the time. Any help would be appreciated. Thanks. Bill
 

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5twins

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Blue is tail light power, yellow is for the brake light. The rear brake light switch is adjustable. Maybe you don't have it set quite right if the brake light isn't working every time.
 

Superdriver

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Blue is tail light power, yellow is for the brake light. The rear brake light switch is adjustable. Maybe you don't have it set quite right if the brake light isn't working every time.
Thank you very much. Just confirming, Blue wire supplies power to the tail light for running light when the key is turned on, and Yellow wire makes the connection from the rear brake light switch to light up the brake light when the lever or peddle is activated. The schematic shows what appears, if I'm seeing it correctly, to be a larger filament for the yellow wire which makes sense as the light becomes much brighter I did not realize that the switch was adjustable. Do you know how to Adjust that as it may be the cause of the intermittent problem. This whole experience has been great as I am learning soo much about how electricity works. Thanks. Bill
Blue is tail light power, yellow is for the brake light. The rear brake light switch is adjustable. Maybe you don't have it set quite right if the brake light isn't working every time.
Thank u again 5twins. I cleaned the connections (very dirty) and adjusted the rear brake light switch sensitivity. Brake light works fine now. LOL, I would never have thought of that if you hadn't mentioned it. Something new learned and experience gained. Take care. Bill
 

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Calliway

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If you have a multi meter you can turn it to the 12V DC postion and take your black lead and ground it to the fender or to the black wire receptical on the bike side of the harness. Then turn the key on and on the bike side probe the one of the other two wires. One will have constant 12V and the is the running/license plate light wire. The other will only have power when you squeeze the brake lever or press the brake foot pedal. Other posters have summed up the rest. Cheers!
 

Superdriver

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If you have a multi meter you can turn it to the 12V DC postion and take your black lead and ground it to the fender or to the black wire receptical on the bike side of the harness. Then turn the key on and on the bike side probe the one of the other two wires. One will have constant 12V and the is the running/license plate light wire. The other will only have power when you squeeze the brake lever or press the brake foot pedal. Other posters have summed up the rest. Cheers!
Thank you very much .I have a multimeter and will do that. Take care. Bill
 
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