Honest answer is that I don’t know and was even hesitant to reply.
But I do know that I’ve been on what looks to be a similar era searay 330 or 340 (can’t quite remember which exactly) with twin 5.7 shaft drive mercruiser and it didn’t have this specific button there.
I’d take a guess that this isn’t original and would perhaps be for an add on thing like an auxiliary instrument like a chart plotter. Might also be a cross over battery link out button for connecting all batteries together for emergency starting of the engine.
Could be a few things really.
I’m interested to know how you get on though. Maybe try and see if you lose anything with it off and not illuminated. It may just be an indication of something like shore power connected or not.
Keep us posted though.
Just an after thought. What else do you have on the boat that might not be there when new ?
Heating, spot lights, instruments etc. The answer will be something along those lines.
No it’s not. It’s the end of the world button. Press it once and a display will appear telling you not to press it again. The world will end if you were to press it a second time.
Or perhaps somebody has already pressed it twice and thats what set of this virus........
It is a throttle cut for when you pass moored yachts-- we wish
Although being Australian, it might be throttle boost for opening times
Or it could be a computerised button that automatically changes one to the motorboat forum when pressed