Brake light troubleshooting

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Gypsie
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Location: Treadin' Lightly under the Clear Blue!
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Brake light troubleshooting

Post by Gypsie » Tue May 21, 2013 10:39 am

I have had an issue pop up, (haven't we all...) wherein my brake lights are not working. I have checked the bulbs and they are intact and should be lighting up.

I am seeking a 'troubleshooting' plan for locating the source of the issue. (Ie first test, then test...)

I have done some checking of the master cyl. light switches by pressing the pedal and checking continuity. One switch closed when the pedal was pressed and one switch did not (I can't remembmber which one at this point). When I did this test my thoughts led me to thinking about the 'primary and secondary' pump circuits and how they interact.
http://www.tegger.com/hondafaq/mastercy ... ematic.gif
(Just FYI for all): http://www.tegger.com/hondafaq/mastercy ... works.html

My thought was that if, during a brake bleed, air got into one of the circuits, would that make it possible for the brake light switches not function and therefore not send electrical signal to the brakelights?

I think that during a brake bleed this happened and is causing this failure.

If so, should I bleed out the master cylinder before moving on to each wheel bleeder (as if it were a new master cylinder being installed and in need of priming)?

Also, If one switch does not work, does that make the whole brake light circuit defunct?

I could get a new master cyl, and switches, though I don't like to fix/replace what ain't broke.
So it all started when I wanted to get better gas mileage....

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drober23
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Re: Brake light troubleshooting

Post by drober23 » Thu May 23, 2013 5:29 am

Gypsie,

97.3% of my light problems turn out to be bad grounds. I would go over all the grounds in the light cluster back there. Then I might put 12v on the light to make sure it lit (verifying the ground was good) before starting to check other stuff.

Good luck!
DJ

'75 Westfalia, '79 Deluxe
(plus more busses than sense)

In a time of chimpanzees I was a monkey

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Amskeptic
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Re: Brake light troubleshooting

Post by Amskeptic » Thu May 23, 2013 2:52 pm

Gypsie wrote:I am seeking a 'troubleshooting' plan for locating the source of brake lights not function
I think that during a brake bleed this happened and is causing this failure.

Also, If one switch does not work, does that make the whole brake light circuit defunct?
These are pressure switches. If one circuit is not developing *any* pressure, its corresponding switch will not actuate brake lamps.
If the other circuit is developing pressure, it will turn on the brake lights regardless. This is a "parallel" circuit, not a christmas tree lights series circuit.

Insuring good grounds and correct contacts at the bulbs is a key first step, followed by an ignition/ON brakes/ON electrical test at the bulb terminals. Then and only then work back to the connectors at the bulb housing and back to the switches. Check power source to switches.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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