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Author Topic: Faulty brake light  (Read 1145 times)

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Offline crobar

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Faulty brake light
« on: July 07, 2012, 09:09:27 AM »
Went for an inspection the other day and everything was good except my brake light would not illuminate when pulling the front brake lever. it worked on the back brakes and all other lights worked.

any ideas what might be causing that

thanks
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Offline bryanj

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Re: Faulty brake light
« Reply #1 on: July 07, 2012, 09:23:35 AM »
wiring from the pressure switch at the lower tree to the loom or the pressure switch itself
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Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Offline Bodi

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Re: Faulty brake light
« Reply #2 on: July 07, 2012, 09:24:40 AM »
Stock system uses a hydraulic switch on a brakeline fitting thingy below the headlight. This switch closes on brakeline pressure. You can test the wiring by jumpering the two wires to it. If the light comes on you need a new switch.
If not, you have to find what's wrong in the wiring.
If the bike has a braided line from the m/c to the caliper then that switch is obviously not going to work. Usually a new m/c with a built in switch is used then.
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Offline lucky

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Re: Faulty brake light
« Reply #3 on: July 07, 2012, 10:23:31 AM »
Was the ignition switch ON???
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Offline crobar

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Re: Faulty brake light
« Reply #4 on: July 11, 2012, 01:54:47 PM »
Not much experience with electrics. So are you saying check for continuity at the switch? Do I need to open up the line to do that?

Can i get a new switch at auto parts store or is it specific to the bike?
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Offline flybox1

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Re: Faulty brake light
« Reply #5 on: July 11, 2012, 02:26:59 PM »
umm, yeah...what bike is this again?  :o
some CB's have their brake switch secured underneath the brake lever.
squeezing the brake lever releases pressure on the switch, activating the light.
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

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Offline phil71

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Re: Faulty brake light
« Reply #6 on: July 11, 2012, 02:43:08 PM »
Lucky, is that a joke?
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Offline crobar

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Re: Faulty brake light
« Reply #7 on: July 11, 2012, 03:05:31 PM »
It's a 78 cb550
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Offline phil71

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Re: Faulty brake light
« Reply #8 on: July 11, 2012, 03:28:36 PM »
on the right side of the lower tree, you'll find this > http://www.cb750supply.com/parts/480/29-7021.jpg
chances are, one of the leads just pulled off the connector. Happens all the time when you turn the bars.
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Offline Sniper X

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Re: Faulty brake light
« Reply #9 on: July 11, 2012, 03:50:26 PM »
is it the same on the 73 350F? Mine doesn't work either. I was just about to chase it down too! Glad I saw this thread.
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Offline crobar

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Re: Faulty brake light
« Reply #10 on: July 11, 2012, 04:54:34 PM »
Nice one. Just had a look, it wasn't the plugs so I'll try a new switch. Am I right to assume it would be the same switch for the 750 as the 550?
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Offline phil71

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Re: Faulty brake light
« Reply #11 on: July 12, 2012, 06:51:08 AM »
Yeah it is. I actually think a ton of fords use the same one too, and any auto zone should have it. Bring the old one , and match it up. Double check the thread pitch against themselves.
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Offline Bodi

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Re: Faulty brake light
« Reply #12 on: July 12, 2012, 07:19:07 PM »
To test, take the two wires off the switch (they just pull off, bullet type connectors) and use a short piece of wire poked in the wire connectors to join them electrically. Then the brake light should be on (key ON of course).
brake light on = bad switch
brake light off = bad wiring (possibly a bad switch as well)
To test the switch, connect an ohmeter across the switch terminal posts. The reading should be very high with no brake applied and should drop a lot when the brake lever is pulled, down to 1 ohm or less if your meter is accurate.
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