Beyond frustrated

[Dieseldude]

As others have said, you probably have a high resistance in the circuit. Voltage present at the load (the LED) is only part of the story. Current is the other factor, and obviously sufficient current is not flowing. To find this resistance, you can examine all accessible terminations between the breaker panel and the LED terminals, the light switch being one of them. It is quite common for light switch contacts to develop high resistance.


Modern silent light switches made for 120 volts AC are not a good choice for DC lighting. The old style that make an audible click sound are more durable for DC. Just ask anyone who has good experience with off grid systems. Do not forget that the breaker itself can develop high resistance, so it should be tested. This can simply be done by swapping your light circuit to a known good breaker.


If all accessible terminations test good, you can run a long test wire from the breaker as an extension for your ohm meter leads, and measure the resistance of each conductor for the light circuit. One wire will likely read quite a bit higher then the normal residual resistance of the wire. If in doubt, determine the gauge of your wires, and consult a wire resistance chart to find ohms per unit of length. Estimate the wire length and do the math. You will need to include your test wire resistance in the calculation.


If no accessible terminations are at fault, unfortunately, you are looking at fishing a new wire. Perhaps opting for surface wiring enclosed in a surface mount wire mold conduit is the easiest option, rather then dismantling interior panels.


High resistances in wiring can be a fire hazard. The resistance can become a hot spot and ignite wire insulation and close by materials. Such a fault should be corrected before using the circuit.


A tip for tracing wires: A piece of test equipment that non electricians might not know about is a "Fox & Hound" or generically known as a "toner". One part is a low power radio transmitter that is clipped to one wire conductor under test, and the wire will function as an antenna. The other part is a radio receiver. The receiver is moved along the wire under test. When close to the wire, it makes an audible tone. If there is a break in the wire, the tone will not be audible past the break. The limit on this equipment is that it will not work through shielded wires and metal barriers. Reception range between the wire under test and receiver is only a few inches. Cost of a set is not outrageous. You might find one for less than a hundred bucks. They are a convenient means of tracing wires that cannot be visually traced. There are many makes and models ranging from cheap and basic to expensive with many features.


Another tip for finding a damaged section of wire: Think back to any modifications or repairs that might have been made near the path of the wire. During the work, the wire might have been damaged, so the area of any work is a good place to start looking.



Good luck

[Bucket]

Lake Effect: You are correct. LEDs have a forward voltage of about 1.6V. Design will include a current limiting resistor in series (in the assembly) that ‘sets’ the nominal voltage. (Vin.max - 1.6v) / LED current= R


What I believe the problem from the OP is is that the wire is not a low resistance path to the battery. There is either a fault in the wire or a poor connection. If that path presents something like 500 ohms of resistance, that resistance is creating a voltage divider with the resistor in the LED assembly and the voltage being presented to the LED assembly is substantially lower.

You connected directly to the battery and it works. You connected it through a length of wire and it does not work. It is very easy to arrive at the conclusion that there is a problem with the wire.

Best of luck!
Mike

[David Mathis]

Disregard the voltmeter, it isn’t indicating available amperage. Try a test light with an incandescent bulb, they look like an ice pick with a wire in the handle. Clean the socket. If that doesn’t cure the problem, run a jumper ground to the socket. Usually, if it’s a wiring problem in a boat, the ground wire, rather than the positive wire, is the problem. If the socket is clean, the connections are good and the ground isn’t the problem, run a jumper wire from the battery to the socket. If that cures the issue, it’s either the hot wire or the switch.

[sailorladd]

Have you tried taking two separate wires off the battery, - and + and connect it directly to the LED light to see if it works, if so you might consider weaving in from the circuit breaker board to the light a new positive wire, and make sure your ground that you are using is well grounded...



When all else fails.....

[IanTrail]

Probably a high resistance like everyone says but in case not, here's my story:

My anchor light is mounted on my stern gantry (The ball must be in the forepart of the vessel but the all-round white can be mounted anywhere best seen). The old incandescent light worked fine but was an unwelcome current draw so I bought a nice LED one.

I swapped it with the old one, turned on the switch and......nothing happened. I checked for 12v at the socket: OK. I checked the polarity: OK. So I took it down below and plugged it into a socket at the chart table: it lit up beautifully. So I re-checked everything at the gantry socket, plugged the LED light in and still nothing. I went around this loop a few times before a little suspicion formed in my head. With the light on the gantry (not working), I covered it with a towel and hey-presto it came on! I didn't realise that the new anchor light had a photocell so it only came on the dark. Down below was just gloomy enough to make it come on.

[Dieseldude]

Re: IanTrail's LED anchor light:
Even "simple" gadgets are no longer simple these days, not even a light bulb. It feels like in insult to one's intelligence to have to read instructions just to turn on a light. We are burdened with study to use even the most basic "smart" gadgets to outsmart them. Recently, I had to read the owner's manual of a rental car just to find the release switch for the fuel tank hatch cover. Imagine that, sitting at a gas station at night leafing through a thick book, trying to imagine if it is indexed under fuel, gas, petrol, fluids, security, etc. The good old days of using common sense, experience, and instinct for many tasks are sadly gone.


A draw back to the photo cell controlled anchor light is that background light might keep it off when it is needed. When it is off by photo cell control during the day, perhaps nobody will think to turn off the switch. Then at night it will turn itself on without anyone knowing. This can be quite an unsafe situation. I would consider disabling the photo cell control so that it functions by the switch alone. Just keep some black electrical tape over the photo cell. The skipper should be in control of essential equipment, not the equipment in control of the skipper.

[skenn_ie]

Originally Posted by pas63

I'm not a marine electrician, but I've done my share of wiring boats and houses. I have an issue that makes absolutely no sense. I have an LED light I'm connecting to factory wiring.

What voltage do you see at the connector closest to the LEDs whem the LEDs are connected and switched on ?
Connect the negative meter lead to the buss bar or battery negative with a long wire. Measure voltage to plus and minus at the LEDs.

[Dieseldude]

Don't forget your grounds. Does the light circuit have two wires, one being a ground wire that ultimately connects to a ground rail that connects back to the battery negative post? Or is the circuit a single supply wire ? If a single wire, the ground path through metal structure and back to to the battery negative terminal could have a high resistance. The ground side of the light terminal should be checked that it measures close to zero ohms.

[Capt MikeC]

I had a similar problem with my running lights. Long story short it was the circuit breaker. When I removed the wire to the running lights from the circuit breaker it showed full voltage, but with the load it was close to zero. I temporary moved the running lights connector to the anchor light circuit breaker as a test, it worked fine. Until I am able to find a new matching circuit breaker to replace the bad one on the main power panel I have the running lights connected to a spare circuit breaker on a small breaker panel I added for other new loads (boat WIFI, TV/DVD, etc.). From the description I could not tell if the circuit breaker was tested or not or if the troubled wire is on its own circuit breaker or if the circuit breaker feeds more than this one wire, but just in case.

[Chotu]

Illogical gremlins are very frustrating.

I just had a similar problem on my RV. The trailer lights weren’t working. I checked all the wires, the fuse, you name it.

Nothing worked.

One day, just for the hell of it, I swapped out the non-blown trailer fuse with a neighbor fuse of the same size.

The lights started working!

Even though the fuse wasn’t blown, it somehow stopped working. The bridge inside was fine, no burn marks, just a mystery.

[betwys1]

Originally Posted by pas63

I'm not a marine electrician, but I've done my share of wiring boats and houses. I have an issue that makes absolutely no sense. I have an LED light I'm connecting to factory wiring.

Wire up the light, nothing. I check the voltage, 12.7V, more than enough for an LED light. Polarity is correct, so I temporarily connect it straight to supply voltage and get light, so the light is good. Hook up the volt meter, 12.7V, lower than the panel (14.6v), but it is probably a 20-30' run over 14 ga wire. Turn the breaker off, check the VM, .1V. Turn the breaker back on and back to 12.7V. Reconnect the light, nothing. Where it gets really bizarre is I can short the pos and neg leads feeding the light and no firework or popped breaker which tells me I don't have voltage but the damn VM does show voltage. I assume it accurate because I have a panel meter and when I check the voltage at the panel with the volt meter it's within .1V of the panel meter.

None of this makes any sense. Tracing the wire is all but impossible sine it's in a bundle, routes through some inaccessible areas. I hate to run more wire. Tempted to just tie it into the courtesy light and be done with it. I'm done screwing with it tonight. Maybe clearer heads will prevail tomorrow.

First: grasp the idea that there is an open or near open somewhere.
You COULD give up and run a new wire OR
buy a cable tracker like this:
https://tinyurl.com/58andv6r about $25