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Tech help needed: brake light brainstorm...

Discussion in 'Technical and Troubleshooting Torque' started by Loz, Jan 2, 2008.

  1. Guys

    Opening this one up to the brains trust - setup is a bit complicated but here goes:

    Tail lights were working fine, brake lights weren't at all from either switch. Bulbs were fine, fuses were fine.

    I found a disconnected spring at the rear brake light switch, put that back together and now the brake light works fine from the rear lever. Excellent.

    This is odd though, the front brake lever isn't turning the brake light on - what were the chances that both brake light switches were rooted?!?

    Took the front brake light switch off the switchblock, cleaned it up with WD40 and did a quick multimeter test. Yes, it's an open circuit when the tab isn't pushed in, and a closed circuit when it is. Connect that to the wires though, and push the tab in, and I get no brake light love.

    So the switch itself is fine, as are the bulbs and the fuse, 'cos it's working from the back brake light switch... I followed the front switch wires back into the switchblock and it all goes into the loom and off into the frame. I can't see any connection issues.

    I haven't farted about with any wiring lately... Any ideas what the problem might be? Bonus points for a quick 'n' easy magic bullet solution! Added degree of difficulty: I'm almost completely useless with a multimeter, so any solution that involves one will have to be explained as if to a 2-year-old.

    Thanks in advance!
  2. So guessing you don't know how to measure voltage with a multi-meter then?

    Try putting the switch back in and hooking it back up to the power (or direct to a battery if possible) then test the outputs like you did for resistance but this time with the multi-meter set for volts (probably be a setting for 20V labelled DC or with a straight line not a wavy one). If no power leaves the switch when it's supposed to then the problems between there and the battery, if there is power then most likely it's a damaged wire between the switch and the globe (look for any part of the cabling that might have become kinked or stretched).
  3. Hi Loz,

    The replacement of the spring on the rear brake pedal I think is a clue. I would think it is a poor earth and the brakes may be being earthed back through that spring. Have you got a wiring diagram for the bike? Usually the owners manual has a poor quality one in the back.
  4. CJ: Yes I've got a wiring diagram... Don't know what it all means though. Far as I can see, one output goes straight to the globe in parallel with the rear switch, and the other goes to the globe in series with the ignition switch, through the #3 fuse and in parallel with the other rear brake switch.

    Does your earthing theory still work if the rear brake switch is now functioning correctly? The spring simply kept the sensor switch under tension so that when you press the pedal, it pulls the switch on.

    JD: I'll give it a crack...
  5. to add visual to jd's suggestion, here is a typical (cheapo) multimeter, with the bit where you want it switched to marked.
    the side that has ~v is for AC voltage, dont use that side.

  6. Righto, got a reading of 0.5 on one of the wires, which I assume means power's coming through to the switch. it also makes it out the other end of the switch like it should.
  7. 0.5 is bad, should read aprox battery voltage
    you have a buggered wire/earth between the switchblock and the bulb.
  8. you've checked the switchblock, next is to isolate where the crack is.
    here are some further locations to poke the multimeter around.
    note - checking continuity is exactly the same as how you tested the switch.
    or just use the ohm section of the MM.
  9. Arr yeah I just worked that out by checking how much power was coming out of the rear switch supply, which puts out around 11.5 volts.

    Bastard. I'm gonna have to pull the buggering tank off and fartarse around with the loom.

    Or maybe just install a plaque saying "stopping" under my bellypan and resolve to hoik up an endo at every braking opportunity.
  10. Mmmm... Doesn't it mean there's an issue between the battery and the leads that go into the switchblock?
  11. to test that, jam the red multimeter lead in the switchblock (ignition on) and put the black one on clean part of the frame.
    try both holes at the switch, coz one will go to the bulb.
  12. Yeah, that's what I did. One lead to the switch gives nothing (I assume this is the bulb-side lead) and the other gives a piffling 0.5v (I assume this one's the one coming from the battery via whatever it goes through.)

    So I guess now it's a case of try to work out where along the line the thing is cut or crushed... Or try to work out where I can splice a new bit of wire in to the loom...
  13. Loz is this a carry-over from the accident on the Lock Up Tour? Perhaps a wire got pinched and it's taken this long to earth out, or break??
  14. I dunno Paul, I've got no idea how long the brake light hasn't been working for, and since I often use the rear brake I wouldn't be surprised if nobody noticed to tell me until IsleOfCam tapped me on the shoulder the other night.

    I like your thinking though... Let's bill Woodsy! :p :LOL:
  15. Er, well after fiddle-arsing about with it some more, disconnecting and reconnecting stuff and spraying lots of WD-40 about the place, I gave up, said "bollocks to you and ya woofta brake light" and put the bike back together.

    And as soon as I did, the brake lights worked perfectly again from both switches.


    Now I have no idea what fixed it or why, or whether it's likely to play up again. So it's working, but I feel justice has not yet been done.

    Thanks lads for your help!
  16. run a new wire (with an inline 10A fuse as close as possible to the battery), straight from the positive battery terminal, cut it in to the side of the connector showing the 0.5v, and if it works, electrical tape it up :grin:
    thats what i'd do for an easy fix.
    or, pull out the fuse box, and run a new wire from the stop/tail fuse holster and bung it in to the connector as above.
    i HATE undoing spaghetti harnesses, so always rerun another line :LOL:
  17. Good to hear its back working Loz, its always a pain though when you don't identify the cause. Looks like you will have to be in front on rides purely for testing and technical reasons. :)