Thanks for the link. But our fixtures use a lamp with a large, single contact, bayonet base with one very large lug and one small one at two different heights from the bottom of the base. Our marine electric store can get the original incandescent lamp for us but it is a special order item. He said this base has not ben used for ages so none of the LED replacement bulb people have had any reason to make a replacement for this bulb because there are so few out there anymore.
If the power consumption was anything we cared about we would change the six fixtures on the boat that use these lamps rather than cobble up some sort of adapter with a soldering gun. But power consumption is not an issue, so as long as we can get the original-style bulbs we'll just keep using what we've got.
