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Old 06-08-2009, 12:42   #1
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Multimeter Reads 12.8v Throughout Circuit - But No Lights!

I have a cabin light circuit that is not working. Tested it and it shows power at 12.8V all the way through and down to the leads off the individual light fixtures. Replaced a fixture with one I know is currently working and in good order to check and it wont light up either.

Not sure where to go next?

cheers,
Brian
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Old 06-08-2009, 12:44   #2
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just for a hoot, try changing the bulb.......
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Old 06-08-2009, 12:47   #3
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Did you check the fixture at the contacts for voltage? Did you put the multimeter across the contacts on the bulb and check for continuity?
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Old 06-08-2009, 12:52   #4
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Probably a bad ground.

Steve B.
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Old 06-08-2009, 12:57   #5
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What are you grounding the multimeter to? The negative side or somewhere else on the boat? Put the negative lead of the multimeter to the negative side of the bulb socket. Then put the negative lead of the multimeter to something on the boat that you know has a good ground. Is there a voltage difference? Its a bad ground then.
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Old 06-08-2009, 13:23   #6
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changed the bulb out with known working bulb on all fixtures. Checked the contacts and those are good too. I would like to try this ground check but I have to find something that's close enough to this circuit, give me a minute.

thanks for the replies!

Cheers,
Brian

ps. my neighbor came over and he is dumbfounded too
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Old 06-08-2009, 13:29   #7
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so just checked on a neighboring circuit and it reads 12.8-12.9
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Old 06-08-2009, 13:34   #8
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have you switched over to LED bulbs? If so, they're polarity specific.
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Old 06-08-2009, 13:39   #9
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no LED's. maybe someday but haven't the money for that right now.
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Old 06-08-2009, 14:01   #10
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IF your bulb is good, AND

IF the contacts are clean, AND

You're measuring 12.8V at the bulb, AND

You still have no light, THEN

You must have a bad connection somewhere in the circuit. It's enough to carry the miniscule amount of amperage needed to activate your meter, but not good enough to carry the amperage needed to light the bulb(s).

The problem could be on either the ground or the positive side, or both.

Check your connections, beginning at the battery, then the CPD, the panel, any subpanel, etc.

Bill
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Old 06-08-2009, 14:04   #11
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oops, just rechecked and another location and it measures 12-12.1V. So I have a bad ground? Now I have to trace that back yeah?
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Old 06-08-2009, 14:52   #12
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Quote:
Originally Posted by sognare View Post
oops, just rechecked and another location and it measures 12-12.1V. So I have a bad ground? Now I have to trace that back yeah?
If BOTH sides of the bulb read 12 v from a known good ground, you have to chase the ground return side of the circuit for the bad connection.

Steve B.
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Old 06-08-2009, 17:34   #13
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you have high resistance somewhere.
AS said earlier, you get 12v but when under load (light installed) your voltage will drop to 0
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Old 06-08-2009, 21:30   #14
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not sure exactly which connection or what adjustment did the trick but just started going through the whole system fastening and cleaning up connections and now we have our lights back.

thanks all,
Brian
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Old 06-08-2009, 23:24   #15
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"fastening and cleaning up connections "
Often that's all it takes, a loose screw and some oxidation. You might want to pick up a tube of "silicon high temperature grease" aka "brake grease" or "dielectric grease". Putting just a dab of this on connections and bulb sockets before you close 'em up keeps the corrosion out. And the silicon grease will not migrate and creep the way that Vaseline does.
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