Side light comes on when brake is pressed

Ziggy81scott · Borekit Bruiser Joined: 27 Feb 2015 Karma :

Hi I'm having problems finding the solution to a electrical problem on my Honda cd125 benly, as the subject title says when I press the brake lever or pedal I'm getting the sidelight coming on in the headlight, and it's with or without the engine running.
I'm panicking a bit as I've got the bike booked in for mot tomorrow afternoon Rolling Eyes

, so I'm hoping someone will have the answer to my problem.
Thanks

Fisty · Super Spammer Joined: 11 Apr 2007 Karma :

Try changing the brakelight bulb and then report back.
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iooi · Super Spammer Joined: 14 Jan 2007 Karma :

Bad earth

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Ziggy81scott · Borekit Bruiser Joined: 27 Feb 2015 Karma :

Thanks will check earth and bulb in the morning and get back to you Thumbs Up

ZebraDriver · Scooby Slapper Joined: 13 Feb 2011 Karma :

Make sure nobody has put a single filament bulb in the tail light. I had this once the single contact on the back of the bulb was touching both contacts in the bulbholder. When you pressed the brake it fed power to the tail light and the sidelight.

stirlinggaz · World Chat Champion Joined: 22 Jul 2007 Karma :

Hi,
I have had this on a couple of different bikes.
with all lights off pull brake lever & clocks light up.
on every occasion I have fixed it by cleaning up connectors/plugs & roughening the earth points.

cheers,
GAZ

Andy_Pagin · World Chat Champion Joined: 08 Nov 2010 Karma :

Had this and seen this many times on cars, though only recently modern ones. It's always due to a bad connector, usually an earth. The leccy can't use it's preferred route to earth so it finds it way there some other way through the wiring, illuminating any bulbs that are in it's path.
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stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

I think the tail lights on that bike may well earth to a ring terminal under the bolt holding the rear mudguard to the subframe. It'll probably be rusty as hell.
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Ziggy81scott · Borekit Bruiser Joined: 27 Feb 2015 Karma :

Checked the bulb and it's fine, replaced it anyway and didn't make any difference so checked earths, they are ok.
My guess is the wiring is fucked, I could burn the fucking thing right now Crying or Very sad

Andy_Pagin · World Chat Champion Joined: 08 Nov 2010 Karma :

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Ziggy81scott · Borekit Bruiser Joined: 27 Feb 2015 Karma :

Took them off and rubbed with emery paper as you say, however one which is riveted I couldn't take apart but I'm getting continuity down the circuit.
I'm worried because the wiring has obviously been replaced around the back end so I've got to wonder about the accuracy of the wiring.
Looked like it's going to have to be checked thoroughly by someone who knows more about electrics than me.

Ziggy81scott · Borekit Bruiser Joined: 27 Feb 2015 Karma :

Thank you Stinkwheel, you've made me a happy man again, you're advice has been spot on, the earth on the back light cluster was indeed bad, so it's all fixed Very Happy

and I'm ready for mot Thumbs Up

I would like to thank you all for your advice

Cheers