I get the large wire is less likely to break. so how are the ABYC saying to connect the small wire pig tales that come on most of the new LED light fixtures.
Those wires would be connected with a properly sized step down butt connector and should never see any load..
what about the breaker size, if you use a 15 amp breaker like most panels come with the 14 ga is good but the small pig tale will become fused link at the fixture
An 18 or 20 gauge wire will absolutely not become a fused link to a 15A breaker. The max ampacity tables show 20A for an 18GA wire and they then allow for 150% of that rating. I have physically blown fuses far larger than the ABYC ampacity rating and in a dead short the fuse pops without even heating the wire jacket. As an example I blew a 300A MRBF on 15' of 8GA wire using a liFePO4 battery bank capable of throwing 20,000+ amps into a dead short. The max ampacity for 8GA wire, at 100%, is 80A.... The wire never even got hot before the 300A fuse blew... Of course you can always change a breaker to a 5A or 10A version, and I do this quite often in circuits that can be "loaded" variably such as house lighting with incandescent bulbs, fans etc. or 12V Outlets or nav stations etc.. A nav light circuit will not be variably loaded and won't be pushing 15A for long durations, which could eventually begin to heat the wire. All we are really protecting for in a nav light circuit is a dead short from chafe etc...
end and the smaller wire is still a place for breakage.
Properly installed this wire should never even move let alone take any load.
the smaller wire is more likely to be the one that will chafe through where it passes through the aluminum mast. also not finding that any of the LED lighting fixtures are ABYC approved
A proper install may require those pig tails to be heat shrunk with heavy walled shrink if they pass through something sharp. That pass through should also be de-burred so it is not sharp...
A proper instal of a tri-color or all-round also requires it to be visible yet many are occluded by a wind instrument or VHF whip...
There are many ABYC A-16 / USCG approved nav lights from reputable companies such as Hella, AquaSignal, Lopo, Marine Beam and others... If it says USCG 1nm, 2nm etc. then it also meets ABYC A-16...