Masthead light problem

[scofan]

Hello Group,

I'll try to condense the issue:

Mast light doesn't work. Assumed it was the bulb. Up the mast, checked the bulb, bulb is good. Back to the deck, checked the socket at the base of the mast. Found 12V at the pins in the socket. Puzzling. Seemed like the the fit of the male/female portion was loose so I bought a new socket. While I had it apart, I put a 12 volt battery on the deck, hooked the wires from the mast directly to the battery and presto! mast light was on. So I'm thinking, ok, bad deck socket. So now I have 2 wires from the mast and 2 wires through the roof of the cabin. To make sure I'm on the right track, I check the voltage on the 2 wires from the cabin..yep 12V. Now I twist the wires from the cabin to the 2 wires from the mast (no deck socket), just to ensure everything works. NO mastlight. Not only is there no light but there are no volts at my wire connections either. Zero. The fuse did NOT blow. The switch in the cabin checks ok as does the fuse and fuse holder. When I disconnect the wires from the mast, I again have 12 volts on the 2 wires from the cabin. Probably something simple but darned if I can figure it out. I'm about to re-wire the entire circuit from the switch panel to
the deck socket. But I hope there is a better way.

I just re-read what I wrote, it doesn't seem possible, but that's exactly what's happening.

Thoughts? Thanks!

Scott in Key Largo

[mitiempo]

If you make a connection very tenuously, say with one strand of good multi strand wire, you will measure 12 volts. But the one strand is not able to carry a load when the light is turned on. It is like trying to fill a water tank with a hose measuring 1 mm inside - yes there is flow but oh so little.

I would check the connections from the deck back to the panel. I think that is the only reason the light doesn't work. You know the mast wiring is ok because you tested it with a battery.

[thehardaground]

Being a boat my first guess would be that the ground connection is probably corroded. Honestly, it's probably just as quick to just run a new pair from your switch to the deck fitting as troubleshooting it and you'll know that it's done right.

[mitiempo]

On some boats there is not easy (or any) access to the wires along their entire length. If they are fixed in place somewhere inaccessible it becomes a big job. But if access is good a new run to the panel would be my first choice as well.

[btrayfors]

Is your masthead light an LED? Some of these are sensitive to polarity, i.e., you must connect positive-to-positive.

Bill

[scofan]

Thanks for all the replies so far. No, it's not an LED Bill. Wish it was though! I'm thinking I have a somewhat major re-wiring project looming. Boats a 1980 so it's probably due, and as the one reply said it's probably the ground side. I just hope I'm not opening Pandora's box...

Scott in Key Largo

[btrayfors]

Bummer.

One more thing to try before you rip it all out: it could well be a simple case of surface corrosion. Suggest you go over the complete circuit very carefully, inspecting and cleaning all contact points: switches, terminal blocks, fuses and breakers, connectors, lamp sockets, etc. Be sure they're all clean and tight. Use some De-Ox It, or similar electrical cleaning preparation.

If you have Buss type fuses, replace them...even if they check good with a voltmeter. Sometimes they deteriorate to the point where they'll pass a tiny current which will be enough for the meter, but can't pass a larger current to operate the light or other device.

You just might get lucky :-)

BTW, age of wiring -- by itself -- isn't likely to be a problem. More likely is corrosion, damage to insulation, and physical weaknesses at, e.g., connectors. The wire itself might be fine.

Good luck!

Bill

[sailingdog]

Originally Posted by btrayfors

Is your masthead light an LED? Some of these are sensitive to polarity, i.e., you must connect positive-to-positive.

Bill

AFAIK, all the LED fixtures are polarity sensitive.

[HUGOSALT]

Had same situation with my vhf radio this fall...12 volts at last connection before radio but no radio. Radio worked with alternate power source. My friend Tom, an
electrical/sound guy came down for an afternoon sail and saw my voltmeter out. When I explained he confidently said I should check connections and for
corrosion, as current was coming through but not enough (same as betrayfors in post # 7 and others above) and I should start from radio going back to panel.
After cleaning and reconnecting 1st connector radio worked.
Still on my winter to do list is to change the 25 year old
wire all the way back to panel. Let's see what gets done!
Hugo

[hellosailor]

Here's one more fast confirmation test:
Take a 12v light bulb, hold it onto the power fittings where they enter the deck/socket. Does it light up? Probably not, even though the meter shows 12v, if the real problem is some corrosion, etc. preventing enough current from flowing.
If the wires are blackened or greenish--they're punked out and you'll want to replace the wire run in any case.