Replacing Cabin Light Fixtures - 12 VOLT?

[jasonislander36]

Greetings everyone, I'm new to the forum but not new to boat questions! I'm seeking some help. BOAT - Islander I36 1979. TO DO- Replacing the interior cabin light fixtures (not just bulbs). Currently they are the original lights, which look to be halogen lights. I just purchased 12v 5" round LED fixtures that fit perfectly over the old locations. HOWEVER, When I removed one of the fixtures yesterday I noticed there are 2 wires leading to the lights - 1 black and 1 white.

The lights I bought are RVZone Marine 12V LED lights. The wires are RED (indicated +) and black.

2 questions here -
1) Will these new 12volt LED lights work when we're hooked up to shore power? Will they work both off shore and on shore?

2) Which of these wires is positive when dealing with WHITE and BLACK? I know the obvious is to get a voltmeter, which I'll do. Our batteries are out of the boat and we're on the hard at the marina still preparing bottom paint, etc. so any suggestions, advice, etc. would be appreciated. Maybe I just carry a marine battery up the ladder, test the white and black wires?

Gratitude to anyone for help!

[Jammer]

1) Your 12v LEDs like the rest of the 12v system will run from shore power via the 12v charger, assuming that your boat is set up in a reasonable way and everything works.



2) Who knows, could be either way for a bunch of reasons. Usually if its black & white then the white is negative. Most (but not all) LED fixtures will work even on reversed polarity,

[GordMay]

Greetings and welcome aboard the CF, Jason.

LED [Light Emitting DIODES] lights are polarity-sensitive. If the voltage is of the wrong polarity, it is said to be reverse-biased, and the LED won’t light.
If your LED light doesn’t light up, after connecting it to your power supply, then simply reverse the wire connections.
I would, most often, expect the White Wire to be Positive, in a Blk/Wht pair - but only testing/tracing will tell, for certain.

I'd TEMPORARILY connect the Red fixture wire, to White boat wire, and Black to Blk. If it doesn't light up, reverse wires. When lit, make permanent connections.

[Spot]

Your best bet is to re-install the battery and check polarity of boat's wiring at each light with a meter, in case the coloring scheme of the wires is not consistent throughout the boat.

I once installed a 12v accessory receptacle (cigarette lighter jack) backwards (reversed polarity) and tested it with an old incandescent meter, which does not confirm polarity, just that there is voltage. I went to plug in a USB charging adapter and immediately 'let the smoke out' of it as the adapter was not made to handle the reversed polarity.

[capt jgw]

The old incandescent lights were not polarity sensitive so it's not uncommon for the boat's wire colors to be incorrect or reversed. Sometimes they even used all the same color wire for lights because it simply didn't matter and was cheaper and easier that way. So as Gord said you'll have to try the wires one way and then reverse if they don't work. You'll need a 12 volt source to do that. You have a 50/50 chance of getting it right the first time and the first try with the polarity wrong will not damage the lights. Some of the really high quality lights have circuitry that corrects the polarity so they work no matter how they're connected.

[jasonislander36]

Thank you everyone for the great information here! I really do appreciate it.
1. I will bring a spare battery on board since our batteries are stored while we're on the hard, and I'll check for polarity on those wires
2. Thank you for confirming that 12v LED lights will work in both AC/DC scenarios (running off the batteries of course, but connected to shore power and thus, batteries remain charged)

I hope you all have a safe and enjoyable spring on the water if you're getting ready to drop in, or have already! It's still a little cold here in Michigan

[JimsCAL]

What I have found to be very handy when working on the boat in the spring when I haven't hauled the batteries from the garage and put them back in the boat is one of those portable jump starters. Just clamp onto the boat cables and I can check the various electrical systems and electronics.

[jasonislander36]

Thank you Jim..that will be my plan, rather than hauling a heavy battery up the ladder. Our boat sits high on the craddle and we're packed in like sardines at the marina so I can't even drop my swim ladder to make the climb easier so hauling a battery in one hand over the rail while standing on the top step of a ladder tied to the boat is a bit of a gamble!

[David Mathis]

Black to black then red to white. The old halogen lights weren't polarity sensitive so they work with the wires connected either way but LEDs won't work with the polarity reversed.

[NorthCoastJoe]

I found these work well with the thin gauge LED light wires going to the heavier wiring in the boat. They are removable too. Use with dielectric grease.

https://www.homedepot.com/p/WAGO-221...B&gclsrc=aw.ds

https://www.autozone.com/greases-and...B&gclsrc=aw.ds