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!)

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 in message
...
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!)

Thanks, sounds like you have a clue! We're just having coffee so it will be
awhile before we start tearing out stuff.

Seahag

"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 in message
...
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!)

use your meter, don't tear anything apart unless the meter indicates the
need to tear out!
Scout

"Seahag" wrote in message
...
Thanks, sounds like you have a clue! We're just having coffee so it will
be
awhile before we start tearing out stuff.

Seahag

"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 in message
...
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!)

Thanks. Just what I was thinking. The new 20w. halogen bulb alone is 0.9
average. The resistance on the ground side is 1.5 ohms. The ground side got
interesting today, I had the terminal strip unhooked to do these tests when
Haggy went to take a shower and there was no water. Why do they use only
one ground circuit for the whole boat? Well I hooked back up... ah marital
bliss restored!

The positive side gives me 255K ohms! I guess we know where the problem is.
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!)

"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!)

Perhaps resistance increases with temperature as it does with almost all
metals.?

Unless the bulb element is made with germanium.

Good going Mr. Hag! Watch out for ground resistance. Daisy chaining ground
wires can give you high ground resistance, or large voltage drops especially
when other circuits draw a big current. If you use multiple devices on the
same ground wire make sure the ground wire is rated for the sum of all the
currents from each device.




"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!)

"Magnum" wrote
Perhaps resistance increases with temperature as it does with almost all
metals.?


Yes, but they most likely have tungsten elements, and will not see such a
*dramatic* increase in resistance (i.e., .9 to 7+ ohms). That drastic
behavior in an incandescent bulb would be very unusual; methinks the .9 ohm
reading is an error.
Scout

Have you read his post carefully? He has stated the high resistance in the
other line, not the ground leg.
Scout

"Magnum" wrote
Good going Mr. Hag! Watch out for ground resistance.

ahh, yes. I stand corrected on that point. Thank you.
Scout

"Magnum" wrote in message
Perhaps resistance increases with temperature as it does with almost all
metals.?

Unless the bulb element is made with germanium.