Re: Raw water pump flow warning buzzer?
These are rare, certainly not a normal factory item either from the engine manufacturer or the boat builder..
As you say it would be simple enough, assuming an appropriately sized (line size and voltage) flow switch can be readily found. You should be able to tie it into the existing multi-point buzzer cct if you can puzzle that out and tie into it.
A pressure switch might be more easily found, more easily installed, and as effective.
EDIT.. belay that last.. it wouldn't detect a plugged passage, as pressure would still be there.. 'doh...
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"