Finding that the socket was not grounding the base of
the bulb fits with the problem as you described it.
Using dual filament bulbs and not grounding one bulb
will causes this. When you applied the brakes and
sent 12 volts to the brake lights, The current path
becomes :
brake light filament, light bulb base (not grounded),
light bulb base to tail light filament to tail light
wire, to other tail light, accross filament and
finally to ground. Each of the three filament will
only drop about 4 volts. If you were to do the math (I
don't want to) you would probably find the the brake
filament drops close to 6 volts while each tail light
filament drop close to 3 volts. 6 volts across the
brake light filament will make it glow, but it will be
dim.
When you turned on the tail lights at the same time
the brake lights were on, that put 12 volts on the
tail light wire. The ungrounded bulb now has 12 volts
on the brake filament and 12 volts on the tail light
filament, since the bulb is not grounded, the will be
no current flow.
The best way to understand what happen is to draw the
lighting circuit showing two wires to each bulb and a
third wire as a ground. Trace the current path with
everything right, then remove the ground from one bulb
and trace the current path.
Hope my explanation makes sense. Sorry about the
techno explanation, but I'm an Electrical Engineer and
can't help myself.
Jim Nordwall
1950 3100
--- chuck clark <cachomeimp@hotmail.com> wrote:
> Had some time to work on my panel truck taillight
> problem today. Ran
> seperate wires to the lights from a point before the
> left tail light door
> contact. No right brake light where I had some
> brake light before. Played
> aroung with the bulb and found that it would light
> by jiggling it. Scraped
> the inside of the socket with my pocket knife and
> presto, I had lights.
> Apparently when I sprayed the inside of the light
> housing with silver
> refelective paint, in order to give me brighter
> light in the rear, I built
> up quite a layer inside the bulb socket as well.
> This build up prevented
> the bulb from grounding. I now have the right light
> in the right place at
> the right time.
>
> However, I do not understand why I had any lights on
> the right side at all
> becasue of the bad ground and why the lack of the
> bulb ground made the
> lights act the way they did, especially the right
> side light going dark when
> both lights were powered. I would still like to
> understand what was going
> on. ANy insights would be helpful.
__________________________________________________
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