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Honda Brake Lamp fail sensor - PBB
I have a 1988 Honda Accord, which is still battling on. It has a very useful brake lamp sensor, that tells me when one of the brake lamps has failed (it would be even better if it told me which one, but one can't be fussy, and the wife is very good at standing behind the car when necessary to pronounce the faulty one!).

Anyway, I was wondering if any technical persons know how the fail sensor actually works?

Thanks
Honda Brake Lamp fail sensor - Dorian
My brother explained this to me once many moons ago, so I'll try to remember what he said:

One wire for each brake lamp is wound around a magnetic switch. The wires are wound opposite to each other. When the brakes are applied, a magnetic field is set up within the switch. If power flows along both wires, the magnetic field is cancelled out, so the switch does not activate. If one lamp is gone, the magnetic field created is enough to trigger the switch and light the warning light.

As I said, this is only what I remember, and its a VERY long time since I did Physics at school...

Honda Brake Lamp fail sensor - PBB
Thanks Dorian for your info. Appreciated. Clever stuff!

As a kid I would often take things apart to see how they worked. Fortunately I've stopped doing that nowadays!
Honda Brake Lamp fail sensor - Dorian
I stopped doing that when it was me that paid for it in the first place!!!