Rear brake light always on

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Mark Tierney

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I hope someone has had this issue before and can help save my sanity. I rebuilt my 1980 xs650 special SG and finally fired it up. Runs great but for some reason my rear brake light is always "On". I thought that I reversed a wire connector between the yellow and the blue at some point, but I went over every connection and can't isolate the issue. Most connections go through a connector and they all seem right. I replaced the ignition switch, front brake switch, rear brake switch, and headlight. I have unhooked the front and rear brake switches and still the same issue. Everything else works fine.

Any thoughts? Any help appreciated.

Mark
 
Your brake light is on with the front and rear brake switches disconnected? Is the light socket stock? Did anyone possibly rewire it internally, or take it apart and get the bottom board in it 180 out? Seems like if that was the case you could watch the brake lever and pedal cycle the lower power element.
 
Thanks for the reply. Yes the brake is on when both of the switches are disconnected. The rear socket is stock - actually two of them. My original and a backup. That is what is so frustrating. It goes right to "brake on" when I turn the key. It must be getting full hot on the rear light wire without turning the bike on. Odd that everything works we'll except for this. I had to splice/repair one of the white wires from the alternator during rebuild since the chain had chewed through almost all of it. Other than that everything went back together normally. I'm at a loss right now.
 
The only thing I can think of, is at the tail/brake light the tail and brake light wires are reversed.
At the tail light the blue wire is the tail light, the yellow the brake.
Maybe for some reason the wires are crossed some where you can't find. Try swapping the yellow and blue.
As long as it works the wire color doesn't really matter.
Leo
 
Just had another thought, have you checked the bulbs? Perhaps the bulb is an 1156 bulb instead of an 1157. I had an old Chevy LUV pickup. It was a foreign made truck that Chevy sold. This had a separate turn signal. Some one had forced an 1156 bulb into an 1157 socket. I noticed the problem as soon as it got started getting dark out. It was just dark enough so that when I stepped on the brake the dash lights lit.
The 1156 is a single element bulb, the 1157 a two element bulb.
The single spot on the base of the bulb when forced into the 1157 socket touched both contacts in the socket, back feeding the brake light into the other lighting and lit the dash light. Never would have noticed if I turned the lights on before it got so dark.
Maybe, maybe not, just a thought.
Leo
 
I am sure I read somewhere on this site that the rear light is wired to be permanently on ,mine is always on,are you sure it is the brake light that is on and not the running light ?
 
+1 on yellowdogs question.
It would be the shorter element for the tail light, longer element for the brake.
 
Thanks. I rechecked everything today, including the bulbs. They are the correct ones. I started chasing the wires and found that both blue and yellow were hot with the key turned. As a last thought, I just hooked up the old front brake switch and they now work properly with front brake ( blue hot with key, yellow hot with brake lever). Now rear brake switch doesn't appear to work. What are the chances that both new switches are defective? Front definitely, back I can't get to work at all. Will check for current once the battery recharges...

Stay tuned and thanks for the help.
 
Easy way to check a switch is to hook a meter to the leads. Set the meter to low ohms. Hook one test lead to each wire coming from switch. Operate the switch. A brake switch turns on the circuit. with no pressure on the brake pedal you should get an infinity reading, step on the pedal it should go to low ohms.
another thing, is the rear brake switch adjusted right? It should be adjusted so when the pedal is up it has just a bit of slack in the spring connecting the switch to the brake pivot rod. Too tight and the brake light will be on all the time.
Leo
 
Did this switch come from Mikes? If so the "leg" of the spring on the switch side may be too long. Not allowing the switch to be pulled enough to work.
 
weekendrider said:
Did this switch come from Mikes? If so the "leg" of the spring on the switch side may be too long. Not allowing the switch to be pulled enough to work.
Click to expand...

It did come from Mike's. I'll check it today. Hopefully, it is that simple. Frustrating to find after spending all of this time that it is new part malfunction. I also have the old one ( original) that I'll pop on to see if that works.

Thanks.
 
Well, here's the update. I went through every conception and traced every wire involved. Turns out the rear brake switch and the front brake switch - both new - we're defective. Used the old and they worked. Checked and cleaned every connection and every light or bulb connection. All works now again. Hopefully, it stays that way. Thanks for all of your help.

Mark
 

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