They call them ground loops.
A ground loop is formed when a circuit completes through some unintended
path to a ground. When you put power on the 'hot' side of the bulb, if the
conventional path to ground is not available, the power will seek another
path. What happens is that the power flows through the filiment to the case
and back into the second filiment, provided the second filiment some how has
a path to ground. You might get a dim light, or no light at all, depending
on the current flow.
With an accurate circuit diagram it should be possible to tell exactly what
was happening and why.
----- Original Message -----
From: "chuck clark" <cachomeimp@hotmail.com>
To: <cachomeimp@hotmail.com>; <jrdorsey@strato.net>
Cc: <oletrucks@autox.team.net>
Sent: Sunday, December 15, 2002 7:13 PM
Subject: Re: [oletrucks] More on the tail light question.
> 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
> around 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.
>
>
>
>
> >From: "chuck clark" <cachomeimp@hotmail.com>
> >Reply-To: "chuck clark" <cachomeimp@hotmail.com>
> >To: jrdorsey@strato.net
> >CC: oletrucks@autox.team.net
> >Subject: Re: [oletrucks] More on the tail light question.
> >Date: Mon, 09 Dec 2002 21:20:26 -0500
> >
> >John, Joe and Steve, thanks for the insights which I will try in a few
> >days.
> > I think I may also try creating a simple junction box someplace before
> >the
> >wires get to the door contacts and run seperate wires to each side from
> >this
> >junction. I'll let you know what happens.
> >
> >Thanks again for the input.
> >
> >
> >
> >
> >
> > >From: jrdorsey <jrdorsey@strato.net>
> > >Reply-To: jrdorsey <jrdorsey@strato.net>
> > >CC: oletrucks@autox.team.net
> > >Subject: Re: [oletrucks] More on the tail light question.
> > >Date: Sun, 08 Dec 2002 22:55:41 -0500
> > >
> > >Chuck,
> > >I'll be darned if it still doesnt act like a ground problem, except
that
> > >open door stuff.
> > >OK, lets try these things next,
> > >First, if you have another bulb, try it. It weird but a couple of times
> > >I've seen new bulb bad right out of the package.
> > >Second, take the lens off the offending light, and take a temporary
> > >ground wire and touch it to the ouside of the bulb socket while the
> > >light is on. If no difference, try to touch it to the metal side of the
> > >bulb itself while in the socket, there is usually a little bit that
> > >sticks out of the socket.
> > >Third, run a power jumper wire from the BATTERY and touch it to each
> > >contact with the door open, see if both filaments will light.
> > >
> > >I'll think about this and see if I come up with other possibilities.
> > >
> > >chuck clark wrote:
> > > >
> > > > I wrote the other day that I had a problem with my tail lights on my
> >49
> > > > panel. I put an additional rear light on the rear door (right side
> > >light) in
> > > > order to have better brake lights and turn signals. I was having a
> > >problem
> > > > with the new light (right side) not working properly, i.e. the light
> > >goes
> > > > out completely when the lights are on and the brake is applied. The
> > >left
> > > > light works ok when this happens. Also when the brake light is on,
> >the
> > >new
> > > > one is dimmer than the left side or original light.
> > > >
> > > > A couple of responses indicated I had a groung problem. I removed
the
> > >buld
> > > > socket bracket and put in a new set of contacts, ground all the
paint
> > >off of
> > > > the area on the bulb holder bracket where it touches the light
housing
> > >and
> > > > the similar area on the tail light housing. Put it back together and
> > >same
> > > > thing happens. Also ran a seperate ground wire from the tail light
> > > > attaching bolt to the body, by passing the door hinge as a grounding
> > >source,
> > > > but no change. The wires go from the light switch and the brake
switch
> > >back
> > > > to the left side door body contacts and then a wire for each of the
> > >right
> > > > side lights is pigtailed off of that switch.
> > > > A couple more observations on the problem. Whether the brake is on
or
> > >the
> > > > tail light is on in the new light, the same filament is lit, the
> >dimmer
> > >or
> > > > smaller filament. This is the case even if I switch the wires. I
am
> > > > getting voltage (using a test light) through both contacts in the
new
> > >tail
> > > > light bulb socket with the brake light and the tail light on. When
the
> > >bulb
> > > > is in, it just goes blank when both lights are turned on. Also, I
> > >noticed
> > > > that when the left side door contacts are not touching (the left
side
> > >door
> > > > is open) the right side light will not work at all when the door is
> >held
> > > > closed so the right side contacts are closed.
> > > >
> > > > Thank you for any additional insights you may have on this problem.
> > > >
> > > > _________________________________________________________________
> > > > Add photos to your messages with MSN 8. Get 2 months FREE*.
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> > > > oletrucks is devoted to Chevy and GM trucks built between 1941 and
> >1959
> > >
> > >--
> > >John Dorsey
> > >Wauchula FL
> > >http://www.strato.net/~jrdorsey
> > >'49 3800 Chevy Panel
> > >'52 640 GMC Firetruck
> > >oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
> >
> >
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