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Brakelight short? 16 Jul 2015 19:34 #681197

  • Kungfutoast
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Hi everyone,
I am banging my thick skull against a wall right now. Maybe someone can shed some light on the problem, or link me to a post with the answers.

I have a very simple (or so I thought) wiring harness. I based it off of one supplied from OregonMotorcycleParts. See attached photo. I have pretty much reproduced this. By pretty much I mean I don't have a starter. So cross that off the picture.

Here is what is happening. When I turn the key the taillight turns on and the brake light will illuminate when applying the brake. I have the head light on toggle switch. With the headlight off the brake will work. but the moment I switch the head light on I lose the brakelight.... I have run through every combination of rewiring the lights arrangement both at the ignition switch and for going the ignition switch. I bought a new ignition switch, new toggle, checked grounds, etc. and still the dummy light in my head won't come on.

Please Halp! What have I missed.
'76 KZ750B Twin
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Brakelight short? 16 Jul 2015 23:29 #681249

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Kungfutoast wrote: When I turn the key the taillight turns on and the brake light will illuminate when applying the brake. I have the head light on toggle switch. With the headlight off the brake will work. but the moment I switch the head light on I lose the brakelight.... I have run through every combination of rewiring the lights arrangement both at the ignition switch and for going the ignition switch. I bought a new ignition switch, new toggle, checked grounds, etc. and still the dummy light in my head won't come on.

Please Halp! What have I missed.

Based on the function, it sounds like it may not be wired as drawn because if it was, it would work. Somehow the brakelight is getting it's power from the line controlled by the toggle switch. Also make sure you have solid grounds on the brake light and headlight.
1979 KZ-750 Twin

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Brakelight short? 18 Jul 2015 11:19 #681513

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So I went through, and then went through it again. Checked the grounds, checked every connection point for shorts and found nothing wrong. Attached is another image I am just used as a wiring model. It's pretty much in your face simple, just like myself. And still no go on the brake light. It will work when in accessory but the moment I switch over I lose brake light function.

Attachment wiring3-1.jpg not found



Thanks for chiming in Bountyhunter. I dropped the toggle switch. Unplugged each accessory trying to narrow down where the problem is. Leaving me with just the rear light. Am I right in thinking there is to much draw to the tail light when in the On position? Not allowing the brake light to illuminate when activated?
'76 KZ750B Twin
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Brakelight short? 18 Jul 2015 15:55 #681547

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I am not sure I understand the symptoms:

When I turn the key the taillight turns on and the brake light will illuminate when applying the brake. I have the head light on toggle switch. With the headlight off the brake will work. but the moment I switch the head light on I lose the brakelight....


Exacty how did you switch it on? With a toggle only or with turning the ignition switch?

Am I right in thinking there is to much draw to the tail light when in the On position? Not allowing the brake light to illuminate when activated?

Not sure how that's possible. The headlight draws about 45W but the tail (running) is about 8W and the tail (brake) is maybe 16W.
1979 KZ-750 Twin

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Re:Brakelight short? 18 Jul 2015 22:06 #681583

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Sorry for the confusion. I had a toggle switch to turn the headlight on and off. I also have a three position ignition switch. My observation was that when I have the headlight on I lose the brake light function. I removed the toggle switch to eliminate possible shorts.

After wiring to the diagrams shown I still don't have brake light function when the bike is on. It works fine when I'm in the ignitions accessories position.

Hope that shed some light on your confusion.
'76 KZ750B Twin

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Re:Brakelight short? 19 Jul 2015 06:11 #681607

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WARNING: Ignorant questions ahead..........

Where do the tail and brake lights ground?

Is there also a switch for the rear brake?
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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Re:Brakelight short? 19 Jul 2015 15:00 #681668

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Kungfutoast wrote: Sorry for the confusion. I had a toggle switch to turn the headlight on and off. I also have a three position ignition switch. My observation was that when I have the headlight on I lose the brake light function. .


Do you mean you turn the ignition switch to another position and the brake light stops working? If so, it means the switch's contact pattern is not what you think it is.

This is typical with aftermarket ignition switches. I had to rewire the new switch I got. In my case, the ignition (coil) only got power with the switch in the parking light position, not the run position.

FYI: My switch has only OFF (all the way CCW), RUN (which is first CW) and PARKING LIGHT (which is second CW) positions. No accessory. Your switch is not making the connection you need it to since your brake light loses power at the position you think is for running.
1979 KZ-750 Twin

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Brakelight short? 19 Jul 2015 15:11 #681669

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TO ADD: Not sure about the 76 750B, mine is the 79 750B. Mine has a six pin connector I think. Z1 sells a switch that plugs in perfectly and DOES NOT WORK because it makes the wrong connections. Nobody makes a replacement for mine, had to rewire the new switch I got to make it work.
1979 KZ-750 Twin

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Brakelight short? 20 Jul 2015 13:10 #681840

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@TexasKZ,
I have tried a few ways of grounding. To the battery ( - ) and the frame. When grounding to the frame I sanded to raw steel, so no paint. There is only one ground from the tail light. The tail light runs to the foot brake switch and then out to the main power wire. The tail light as a line out to the main power as well.

@BountyHunter,
Do you mean you turn the ignition switch to another position and the brake light stops working? If so, it means the switch's contact pattern is not what you think it is.
I am using and aftermarket switch. I thought this was my problem and bought a second IG from a different brand. Only to have the same problem. :huh: Linked is the second switch I bought. www.dimecitycycles.com/universal-3-posit...ignition-switch.html.

I just tried setting everything up for the different switch positions. My observations are as follows. See attached image for diagrams.

Diagram 1: In position first CW, head light on, tail light on but NO brake indication light. Switching to second position CW same results.

Diagram 2: In position first CW, headlight off, tail light on with functioning brake light. Switch to second position CW, headlight comes on and I lose brake light function.

Diagrams 3 & 4 not shown: I skipped the (L) slot on the ignition switch and plugged everything to the (IG) yielding no positive results. Headlight and tail light constant with no Brake Light function.

Also I did the wiring job - see attached. The PO did his version of a wiring harness and it was way worse than mine. A lot of electrical tape and loose hot wires. Ugh it had to go. But some how he had the lights working... :blink:

I appreciate your help guys. B)
'76 KZ750B Twin
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Brakelight short? 30 Jul 2015 14:49 #683487

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Hi Guys,
Thanks for all the help. I found my problem. There was a poor solder at the tail lights bulb hosing. I removed the wire, soldered onto the bulb housing itself and grounded straight to the frame, solving my problem.

Few that was a frustrating few weeks.
'76 KZ750B Twin

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