anchor light problem

[edbulmer]

On my anchor light there are two bulbs and one stays on partially even when the switch is off. Has anyone heard of this problem and where do you think the problem would be located?

[Albro359]

How are the two bulbs wired...series or parallel ? Two pole switch or single ?Is the return wire used for another light also somewhere ?
The problem will be in the wiring....or maybe one of the bulb connectors is touching something metal ...or ?

[Vasco]

Maybe it's a night light.

[Reefmagnet]

Rear tail / brake lights in cars have similar problems when the socket develops a bad earth which is usually the wire common to both filaments. Without knowing how your lights are wired, look for a bad connection at the circuit where the two bulbs are common wired together.

Led bulbs can also glow dimly as a result of small leakage currents in the circuit (e.g. as may be caused if wired via a solar regulator with night switch function). If this is the case the power draw is next to nothing and can usually be ignored.

[edbulmer]

That was funny, I almost wet myself- "night light" on second thought it is for night use. I'll tell the broker that if I ever sell the boat. Maybe that's a selling point. I"m on Toronto during the summer too.
It is a led, and that is probably what is happening. It's only a faint glow. Probably not worth going through the circuit. it is tied together with my running lights on the same circuit. Maybe I'll go "play" with it.

[Redline452]

I troubleshot a friend's boat when his stern light would not go out, even though the switch and red/green bow lights were off. Maybe it was the tequila, but after a moment's thought I asked if his son had turned on the light in the v-berth, he said "yes but it doesn't work".

His ground was broken somewhere forward of the mast, isolating the what was supposed to be the ground for the front cabin and forward nav lights. The resulting circuit, with the cabin light switched "on", was:

+12V supply to v-berth light "+", v-berth light "-" to fwd nav lights "-", through both nav lights in parallel, nav light "+" to stern nav light "+" finally to stern nav light ground.

With the two forward nav lights in parallel, neither conducted enough current to light noticeably, and the higher wattage / lower resistance of the v-berth cabin light let the stern light get most of the voltage. Added a ground jumper to the fwd cabin light, and voila, no more mystery stern light.

In this case, I'd look for a bad ground, likely at the mast between the lights. I've seen boats wired with two masthead bulbs so the forward one alone serves as a steaming light and both together make an anchor light (at the cost of double the current drain while anchored). The LED bulb might get enough current to light via pilot lights in the electrical panel, if any.

[River Cruiser]

If this is a combination stern / anchor light the rear bulb is on when the nav lights are on. If that's not the type light you have then the reply on the bad grd is probably correct. Good luck

[David M]

It's a voltage drop probably caused by higher than normal resistance in the circuit. Break out your multimeter and check. On boats it is frequently corrosion somewhere.

[edbulmer]

Thanks David. I'm a novice in that area. Can you explain how to do that.

[hellosailor]

ed-
Assuming the switch is in fact working, that could mean the bulb has been wired to a "switched ground" circuit instead of the more normal "switched hot". The switch is interrupting or making a GROUND to the bulbs, when it normally would be supplying or interrupting HOT to the bulbs. You can check that out by testing the power at the switch, see if it is in a hot or ground line.
There are pros and cons to using a switched ground, suffice to say most of the world thinks that is the wrong way to do things. If that's what you have, then all it takes is a short to ground to turn on that bulb, regardless of the switch. So there may be a short in the lead from the bulb to the switch. You could test for that with a multimeter.
Shoulda, woulda, coulda, first step really is to take a multimeter and actually test the wiring, all the wiring in the mast, to find out how it was wired and whether there are shorts in any of it. That's the only sure way to fix the problem completely and correctly the first time around.

[David M]

Originally Posted by edbulmer

Thanks David. I'm a novice in that area. Can you explain how to do that.

First, have you cleaned the contacts in the bulbs socket and the bulb? Second, have you tried putting a different bulb in the socket? I'm just checking to see that you are trying the easiest and most likely potential solutions first. I like putting a little dab of silicon grease on bulb sockets to help prevent future oxidation of the contacts.

To answer your question, what Hellosailor said plus checking the resistance in the circuit between the hot source at the electrical panel and the hot side of the bulb socket and then check the bulb sockets negative side to the ground at the battery. Then check to see if the resistance across the bulb is close to the resistance of the entire circuit with the bulb back in place.

I hope this make sense? You are looking for any resistance in the circuit that should not be there.

You also want to test the voltage across the bulbs socket. It should be very close to the voltage across the switch or breaker for the light.

You also want to confirm that the two bulbs are in parallel with each other, or on their own separate circuits. Two bulbs with two different impedances (resistances) in series with each other can have the effect that you are seeing....one bright and one dim. If someone before you wired the bulbs in series, you are really not supposed to do this and it needs to be fixed.