Message text written by INTERNET:Eganb@aol.com
>I should be able to figure this one out. My backup lights have suddenly
stopped working. With the car in reverse, and both backup bulb holders out
of the taillight assembly, I use my voltmeter and place one lead on the
wire
going to one bulb holder, and the other lead on the metal shell of the
light
assembly.
Sure enough, got 12 volts going through it, but the bulb won't light. If I
test the other bulb holder, same thing. But if I reconnect one bulb holder
to its taillight assembly, then I don't get any voltage going to either
backup light.
All of the rest of the lights work fine. Is it possible to have 12 volts
running to the backup lights, but simply not enough amps, because of some
reason? I assume the amps are what make the bulb light up?
And I assume this isn't a grounding problem, because I assume the taillight
assemblies ground to the body, with only a hot lead going to the bulb
assemblies.
Lots of "assumes" and you know what that means.
Any ideas?
<
Bruce, this phenomenon confuses many folks who are not familiar with
electrical theory. What you have is a high impedence connection in your
reverse lamp circuit, somewhere. When you pull the lamp assemblies out of
the lense assemblies you interupt the ground circuit and no current flows.
When you connect your volt meter your recreate the circuit but the
voltmeter draws a whole bunch less current than your bulbs would had they
been in the circuit, too. When you see voltage without the bulbs and no
voltage with the bulbes it means that there is something upstream limiting
how much current can pass.
Consider this analogy: Connect the hose to your spiggot (faucet) and just
barely crack the valve open so that a mere trickle flows. At the other end
of the hose you will see water trickling out the end but there is no
pressure. Now take your hand and block off the end of the hose. Notice
that the pressure build up to however much pressure you have in the house.
Water pressure is analogous to voltage and water flow is analogous to
current, the open hose is analogous to having the reverse lamps connected
and blocking off the hose is analogous to not having them connected. If
you would have opened the faucet completely you would have had pressure
under all situations.
You have a bad connection somewhere. It could be the switch contacts
themselves. Or it could be any of the many connectors on the way. There
is a four way or five way connector at the fire wall near the bell housing
for the reverse lamp switch harness (and the starter interlock on automatic
equiped cars). If these contacts are the problem, unplugging and
replugging this connector may clean off enough corrosion to rectify the
situation. That is the easiest thing to do.
The next easiest thing is to jumper around the switch - for test purposes
only, the lamps will be on continously as long as the jumper is in place.
If this fixes the problem, replace the switch.
Beyond that there is likely a bad connection somewhere in the harness. In
this case consider leaving them nonfunctional.
Good luck
Dave Massey
/// triumphs@autox.team.net mailing list
/// To unsubscribe send a plain text message to majordomo@autox.team.net
/// with nothing in it but
///
/// unsubscribe triumphs
///
/// or try http://www.team.net/cgi-bin/majorcool
|