I'm not sure to whom you are replying but I'll toss in another 2 cents. If
the bulb is good, as he has stated, and the rest of the circuit is intact,
then a voltmeter is appropriate. True, a voltage reading without a load can
be misleading, but it also a piece in the diagnostic puzzle. Had he the 13
volts present without the bulb (i.e., measured at the fixture's terminals)
and lost the voltage when the bulb was subsequently plugged in, then I would
say he has a complete circuit (proven by the first reading) which is unable
to sustain the current, and therefore the potential, possibly do to a high
resistance in the circuit or a faulty power supply (I think we are all
assuming the power supply is not the problem, however).
Scout

"Magnum" wrote in message
ink.net...
Checking voltages is almost useless because the voltmeter is usually 10
Mega
ohms input impedance or more. It draws no current and will always measure
the open circuit voltage. Resistance is a better measurement or voltage
measured under loaded conditions.
A good battery and a weak battery will give the same voltage reading. They
can't supply the same load current because the weak battery has a higher
internal impedance. Just go and review your Thevinin equivalent circuits.

Magnum

"Scout" wrote in message
...
"Seahag" wrote
The new 20w. halogen bulb alone is 0.9 average.

.9 Ohms? If so, something is wrong here, perhaps with your meter. At .9
ohms, given a 12 volt supply, that bulb would draw 13.3 amps (or 160
watts).
A 20w bulb should have an ohm reading of about 7.2 ohms.


The resistance on the ground side is 1.5 ohms.
from where to where? from the grounded terminal strip to the ground side
of
the bulb socket? That should be closer to zero, but again, I don't know
how
accurate your meter is.

The positive side gives me 255K ohms!
Again, measuring from what point to what point?
One way to double check this before you rip anything apart, is to take a
new
piece of clean, adequately sized wire (14-16 gauge), long enough to
reach
from the fuse or breaker panel that feeds the lights, and do the
following:
1. check the resistance of the new wire (it should be very close to zero
ohms).
2. disconnect the positive wire from the light fixture and twist one end
of
the new wire to the now disconnected fixture wire. make sure they are
clean
and tight.
3. run the other end of the new wire back to the fuse or breaker panel.
4. disconnect the suspect wire from the fuse/breaker and connect your
ohm
meter to these two free ends.
5. if you show high resistance now, break out your saw or find an
alternate
route for your new wire.


I hope this helps. If nothing else, it can confirm suspicions before
ripping
apart anything. I'm a bit concerned about that meter though.
Scout



Too bad the wires are forever berried in epoxy. I have the saw out.
Stay
tuned.

Mr. H.


"Magnum" wrote:

Measure the resistance of the bulb alone. Then measure the
resistance
of
the
wires with the bulb in the socket from the circuit breaker or power
connection. If the bulb is, for instance, 12 watts, it draws 1
ampere.
If
the wire resistance is 5 ohms in addition to the bulb resistance,
you're
looking at a five volt drop in the wires, which is almost the power
of
the
bulb.

Report the resistances of the wires back to me and I'll walk you
through
this.

Magnum

"Seahag" wrote:
So the aft-most two dome lights (12 volt) on a 4 light circuit
have
been
giving me the blues for a month or so. Intermittant most of the
time
but
now dead, sort of... Bill replaced the switch on one and they
both
worked
until he left town...After another day of meters and torn up
galley
seems
he's getting 13 volts through the wires but it won't light the
bulb...He's
thinking there is some sort of resistance somewhere. Any ideas?
Experience? Jokes?? The Taiwanese in their infinite wisdumb
epoxied
the
wires into the deck beams and cabin sides!!!

Seahag
(Dinner's on before dark!)