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Old 20-12-2009, 15:00   #1
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Half the Voltage?

On our trip up to La Paz, the stern nav light suddenly when out. I checked the bow light and it was just fine. When we got into port, I found that the bow showed 12.6 volts while the fixture on the stern only showed 6.2 volts or there about. I've traced the wires down to the deck and all appears fine.

I don't understand how I can be reading just half of what the bow is reading. If there is a break in the line, shouldn't I be reading "0" on my meter? I pulled the wires out of the fixture and checked them and I still get the same reading.

OK, anybody out there have an answer for a clueless sailor?

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Old 20-12-2009, 15:19   #2
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Most likely a corroded connection somewhere that is acting as a resistance approx equal to the bulb resistance. Clean all connections.


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Old 20-12-2009, 15:19   #3
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What colour is the copper inside the wire? nice and shiney or black and corroded. I recon corrosion inside the wire is causing a voltage drop.

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Old 20-12-2009, 15:25   #4
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You have resistance in a connection somewhere. Start at the source of power (breaker, switch) with the light bulb in and the light on and check every connection till you find it. Might be hard to find all the connections. check ground buss bars as well. The fun never stops lol

Good luck
Capt. Wayne Canning, AMS
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Old 20-12-2009, 15:55   #5

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"What colour is the copper inside the wire? "
Well, if the wire looks like copper rather than silver (tinned) then it is time to condemn the wiring and replace it with proper marine-grade tinned wiring. Somewhere in the circuit to the stern light, there's a loose or corroded contact or bad piece of wire. Either in the hot side, ground side, or socket, but somewhere there's a simple physical problem dropping the voltage.
Could be some yoyo twisted wires together and taped them over, instead of making a proper splice too.
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