Pointy - No Brake Lights

[Nutsinatin]

Hi all,
Having a bit of a problem with my 2009 bike where I have no brake lights and hoping someone here might be able to give me a bit of a hand.

• I do have rear lights.
• I have checked that the brake light is not stuck on (rear brake adjuster).
• The pointy has LED rear lights so it's not a blown bulb/ filament.
• Using the front or rear brake lever does not produce light.
• I have checked the connector block under the rear seat - no corrosion and a good connection.
• The horn works so the fuse is good.

Taking readings from the connector under the rear seat with the engine running I have:

• 12v from the brown live
• 0v from the black/white
• 8v from the white/black
• 9.5v from the white/black with the front or rear brake applied.

If anybody could tell me the expected voltage that would be a massive help.
Or if you know what is wrong that would be even better!

The bike has been sat idle outside for the last two months under a cover due to a sheared oil line so it could be a damp connector. I'm just hoping for something a bit more specific before I strip all the plastics off to check every connection.

Thanks guys

[Seeker]

The 12V on the brown makes sense because that's the tail light, the black/wh being the return path to the battery which is why it's 0.

Since the tail light is fed with 12V I would have expected the brake light voltage to also be 12V when one or other brake switches are activated and 0 when they're not with different value internal resistors (in the light housing) to account for the different brightness levels. (I'm guessing).

Out of curiousity, if you disconnect the brake/tail light connector and measure the white/black on the loom side - do you get the same voltages (8 and 9.5) with either switch applied?

... and that has depleted my suggestion bank.

[TamSV]

Worth double double checking it’s not jammed on. If the white/black is the brake then shouldn’t it be zero without either of the switches activated? (I would have thought - guessing though)

Can you disconnect both brake switches altogether just to be certain? Or switch it to parking light and see if it’s dimmer.


EDIT: typing at the same time as Seeker but looks like we’re having an the same thought.

[Bibio]

i'll dive more into it later but there is a block connector inside the headlight cowl under the instrument cluster that furs up. this connector serves the lighting and indicators but i cant remember if it shares power with brake lights.

[Ruffy]

Originally Posted by Seeker

...
Since the tail light is fed with 12V I would have expected the brake light voltage to also be 12V when one or other brake switches are activated and 0 when they're not ...

Originally Posted by TamSV

Worth double double checking it’s not jammed on. If the white/black is the brake then shouldn’t it be zero without either of the switches activated? (I would have thought - guessing though)

Can you disconnect both brake switches altogether just to be certain? ...

This, IMHO too.

From glancing at my K5 wiring diagram, it should be straight 12V (i.e. battery voltage) on the White/Black wire when either switch is pressed on (White/Black is the brake light feed from the switches), and close to Ov when off

It's possible the tail light internals have failed (even LEDs & electronics break down from time to time) but unlikely, as you say, so I suspect a corroded or otherwise gummed up switch. I can't recall how easy it is to disconnect them but that's what I'd be looking to start with: Disconnect both and reconnect each in turn to see if you can isolate the fault. Test each switch with a multimeter if you have one.

From memory, the switches aren't really dismantleable for cleaning but sometimes you can get away with spraying lots of cleaner into the switch via the operating stud and operate them many times to try to dissolve or wash away any crud inside on the contacts, but often it's pretty much replacement time if they're not on/off binary clean.

[Nutsinatin]

Fantastic - thanks for the advice guys - now I know it should be 0 & 12v I'll clean/disconnect the switches at the weekend and see how I get on before trying anything else.

[Bibio]

rear tail light:
Running lights + = Brown (this is constant live when ignition is on).
Brake + = White - Black band (this is only on when a brake switch is on).
Return (ground) = Black - White band (this is for both brake and running lights).

Front brake switch: (the switch cabling can be different colours depending on year of bike. its not till it connects with the main loom that the cabling colours change).
Live feed to switch + = Orange with Black or green band (this is constant live and shared with a few other electrical equipment including the horn).
Switch ON feed + = White with Black band (this is the live out when the brake is on)

Rear brake switch: (the switch cabling can be different colours depending on year of bike. its not till it connects with the main loom that the cabling colours change).
Live feed to switch + = Orange with Black or green band (this is constant live and shared with a few other electrical equipment including the horn).
Switch ON feed + = White with Black band (this is the live out when the brake is on).

its highly unlikely that both switches have failed but hey stranger thing's have happened.

my advice is to disconnect the front brake light switch then the rear and see if the rear light dims. as others have said it could be that a switch is constant on.

good luck.

[Nutsinatin]

Well I got a chance to look at the bike last weekend.
Disconnecting the front brake switch dropped the rogue voltage to 2v and bridging the connector got the brake working again on the front switch. Testing across the switch I had infinite resistance.

Rear brake was a similar story. Bridging lit up the rear light and I had 18,000 ohms resistance across the switch.

Replaced both switches today and instantly fixed everything. I had changed calipers/ fluid before the MOT so I can only deduce that all the extra wear from bleeding followed by a month of sitting idle was enough to finish off the 14 year old electronics.
So it was the rare double switch failure.
Thanks all for your help, much appreciated.

[garynortheast]

Yay, good to hear there was a satisfactory resolution to the problem. Nothing stopping you getting out on it now!