But if you use 10 or 12G wire don't let anyone plug in the search light.
I suspect if you had an issue with a search light and 10 or 12 GA wire it was a corrosion or termination issue??
For example our Brinkman searchlight, one of the most powerful on the market, has a 100W bulb.
100W / 12V = 8.3A
A 30' circuit of 12 GA wire will yield a voltage drop of just 3.3% at 8.3A. The ABYC allowable circuit drop for a "non-critical" circuit like this is 10%. If like on most boats the outlet is near the electrical panel then the wire run from the panel feed to outlet will be but a few feet. Teh panels are normally fed with much larger wire.
The boat I just came from a two 12V outlets at the nav desk. The wires feeding the panel are 1GA and the outlet circuit length is under four feet of wire. It was fed with 12GA from the factory. Even at the full 15A rating of the outlet & breaker his voltage drop would be just 00.82%..
You could go to an 80' long circuit with our very powerful search light with 12GA wire and still be under the allowable 10% voltage drop.
A 30' circuit of 10 GA wire will yield a voltage drop of just 2.1% at 8.3A.
Even with an outlet with a max ampacity of 15A and a 30' circuit of 12GA wire you are still at only 6% voltage drop or 4% below the ABYC allowable limit.....
Many of these "outlets" are max rated at 10A and you really need to dig to find one rated at 15A.. 12GA in most instances is more than adequate and your voltage drop should not be an issue.