I would see if the existing lights could be converted to LED. This place is good Boatlamps - Marine LED bulbs and replacement lamps for all boats for LED bulbs, not the cheapest.
Somewhat hidden Voltage Drop Calculator | 12 Volt Planet Cable Calculator in the knowledge centre section.
Apologies for not answering the question you asked, but if it were my boat I'd be fitting a 3rd switch, so the deck level nav lights could be turned on without the steaming light. This is a) for when the tricolour fails, and b) for sailing in close quarters, where deck level lights are more likely to be seen.
A good reason not to fit one of those is because of the unconventional wiring required. The polarity needs reversing to choose which light you want switched on. That requires switch panel changes for most boats.
I agree, I have put a like to your reply. It would mean a lot of faffing about and it is unlikely I would be sailing at night in a close quarter situation. Thankyou for your reply
They supply the switch prewired. .
Supplied with a single 3 position switch to control 2 lights, which is not how most switch panels are designed, so changes to the switch panel required. The Nasa combo light is not a drop in replacement for other combined masthead lights. If, as on some boats including mine, the masthead all round white is used as both an anchor light and a combined steaming/stern light when motoring then you have no chance of using the unconventional Nasa way of doing things to fit in with the existing panel configuration.
You’re quite right and I haven’t got one in out boat. However it was something for the OP to consider with the advantage of it being relatively cheap.
