[TR] Brake light - update

Randall TR3driver at ca.rr.com
Sun Jun 26 17:41:19 MDT 2011


> Ground wires appear to be good as the lights
> work independently.

Nope, doesn't work that way.  What happens when one fixture is not grounded
is that the current flows one filament to the bulb shell, then because that
is not grounded, it goes back through the other filament in that fixture,
and to ground through the unlit filament in the other fixture.  Effectively
all three filaments are in series, but because an unlit filament has a much
lower resistance than a lit one, only the 'dim' filament comes on (because
it also has higher resistance than the 'bright' filaments).

Almost certainly, either your RH lamp is not grounded, or the bulb isn't
making good electrical contact with the socket.  I had a lot of trouble with
the ground connection between bulb and socket on my 3A, until I cleaned both
surfaces up good with a Scotch-brite pad and then gave them a light coat of
Vaseline.  Be sure to pay attention to the place where the pins on the bulb
rest against the barrel of the socket, since that is effectively the only
place there is contact in that fixture.

-- Randall  


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