Thanks for the replies guys, I found the problem and you were both correct. The saildrive plug
usually just hangs off the port side engine front. On mine I couldn't find it, when I did it was bent back (under the oil
filter) and the white/red wire was tightly squeezed under the lock washer of the foward engine mount...amazing that it took 23 seasons to chafe through the shielding!
BTW I tried just removing the bulb but the alarm
kept on ringing. Glad I found the source, engine alarms often go off at the worst possible time, even though I knew the saildrive
one wasn't applicable to me the sound is still un-nerving.