Brake light problem

Hi Guys, I'm new here (see intro http://xjbikes.com/forums/forums/hangout-lounge.3/create-thread), and I'm sorry to kick off so early in my post count with a question.

Here's the thing, the brake lights on the Seca just stopped working. At first I thought it was just a blown lamp but when I actually looked and saw that there were two lamps I was immediately suspicious that there might be an electrical / wiring issue since what are the chances that both lamps fuse at the same time.

Turns out that the lamps are fine (tested and double checked them). Putting a voltmeter across the wires tells me that there's power when the brake-light switches are activated (strangely there's also just under 4V across the wires when the ignition is on, but I suspect that this is bleeding through from a common earth (ground) somewhere.

I also checked the grounding and that seems to be OK - the lamp holders themselves are not corroded and I checked if they were making good contact by disconnecting the wires and connecting a separate 12V supply.

Your thoughts?

Thanks.

 

check your brake switches (2) and connections could be dirty connections
please put your bike model in your signiture line 1982 750 Seca or XJ750RJ

haynes manual free download
http://www.manualslib.com/manual/837861/Yamaha-Xj750.html

wiring diagram
http://members.tripod.com/dave_jack/wiringdiag/d10a.jpg

http://members.tripod.com/dave_jack/wiringdiag/d10b.jpg

http://members.tripod.com/dave_jack/wiringdiag/d8.jpg

item 27 in wiring diagram is the brake lights and you can see that they share ground with the tail lights which is your 4 volts.
did you check your fuse #9 in the item 6
there seems to be a connector where the yellow wire from the rear brake switch meets the green/yellow wire from the front brake switch near the cluster
also a second connector where the yellow/white wire goes back to the lights check for clean and voltage. continuity
i am just guessing the yellow /white wire it could be blue/white wire but i think that is the tail light.
the diagram shows a greyish color wire carrying the voltage from fuse to switches voltage should be constant 12v at the connectors


almost forgot welcome to the site

 

You link doesn't actually go to your intro.

If this is a Seca model that uses the electronic cluster and warning center, then the brake light circuit (and the tail light circuit) will run through the cluster. This is to sense whether a bulb is burned out.

Have you tried with both the brake lever and brake pedal, to verify it's not just a bad switch?

Could also be a bad connection in the headlight bucket. Or, worst case, it could be a bad warning center module.

 

Thanks XJ550H. I do have those schematics and the switches are functional. According to the diagram the feed runs through the "dash console box" that I think you call the Attari - is it possible that the problem could be here?

Are you referring to the Haynes manual here?

Thanks.

 

colors on posted wire diagram may not be what is on the bike.
refering to the wiring diagram i posted.
#6 is the fuse box #9 is the signal fuse. i would start with the fuse and move forward to the switches following the voltage to each switch "the grayish wire"
are you still using glass fusses? if so you should consider the upgrade

the atari box is a mystery to me but it looks like it can be unplugged for testing the brakes lights
with possible jumpers but I would not try that untill someone confirms if that can be done

the jumper would be between the yellow and yellow/white at the connector

 

Thanks SQLGuy, I don't see where it allows me to edit my post, but here is the correct link http://xjbikes.com/forums/threads/hi-from-sunny-rsa.76814/

This is indeed the Seca model with electronic cluster. (I'm not confident that the cluster is working as it should). Both lever and pedal switches are working. I've looked into the headlight bucket for loose / poor connections and made some repairs there that were necessary, but none related to the brakelight. If worst comes to worst I'm thinking that I might have to bypass the cluster on the brakelight circuit.

 

No, this has already been swapped out for the plug in type fuses by the PO. Oddly there are only 4 fuses in that box, none of which are marked, but I have checked them all.
The rear running lights still work and the rear indicators (blinkers) also work.

I'll study the schematics again and see which sockets of the connector behind the headlight need to be jumped for the brake light and give that a try.

Thanks.

 

it should be this 6 position connector no garentee that the colors are correct on the drawing. ohm them from where they come from,
you will see a green/yellow from front brake and a yellow/white wire from the bulb . red line would be jumper. green/yellow has a yellow wire connected to it from rear brake switch switch . this is indicated by the black dot it may be a seperate connector or at the main 6 position connector

 

Thanks for that, appreciated. Yes, I will disconnect battery and unplug the connectors front and back and then check continuity for which wire is the feed to the brake light before I jump it. According to the schematic, the live feed is consolidated after the two brake lever switches before it gets to the connector, so with a bit of luck I will only have to jump from one wire.