For those of you who are experienced with this sort of thing, I wonder
if we could take a theoretical look at this problem? My first thought when
I heard that the running lights were on when they were supposed to be off,
off when they were supposed to be on, was that whatever is triggering them
was reversed in polarity from normal. However, a lot of folks have pointed
to a ground as a possibility; I did not consider that, but perhaps I should
have. In an attempt to learn more about this, could somebody maybe explain
how this would work exactly? Here is what I have been able to come up with
so far:
Assuming that the running light pin on the truck is actually functioning
correctly, there is no power going through it when the headlight switch is
off, so if the running lights are on, they must be getting power from the
other side, which is normally ground. Running lights typically get their
ground from the trailer's frame, so I am assuming that when the headlight
switch is off, the running light circuit must be grounded somewhere up the
line, and the running lights on the trailer are actually getting their
positive voltage from the frame of the trailer. It would probably have
to be a pretty decent voltage too, for all of the running lights to come
on at full power (Miles didn't mention that they were dim, so I am assuming
they were basically at normal brightness.) The assumption then would be
that when the headlight switch is on, voltage is applied to the running light
circuit which means that the running lights have +12v on both sides, resulting
in them not lighting up. So, my question would then be, how is this +12v
leaking into the trailer frame, and why wouldn't having the frame of the trailer
energized also prevent other lights such as the stop and turn signal lamps
from lighting? I am assuming they would share the same ground plane as the
running lights.
Any ideas? (Note: this actually isn't a sarcastic post trying to
disprove the theory that Miles' problem is a bad ground, I am genuinely
curious and would like to learn how a bad ground could cause this
phenomenon, as I think it would be quite instructive, and helpful to
myself to diagnose similar problems I may come across in the future.)
Thanks!
--
-Jon-
.-- Jon Steiger ---- jon@dakota-truck.net or jon@jonsteiger.com --.
| 67 Coronet, 70 Cuda, 90 Dakota 'vert, 92 Ram 4x4, 96 Dakota |
| 96 Intruder 1400, 96 Kolb FireFly, 99 Cherokee, 01 Ram 3500 CTD |
`------------------------------------ http://www.jonsteiger.com --'
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