If the boat runs Borg Warner gauges, they are servo driven off a computer box called an MDDC. Both signals come out of there, it's probably bad.
You may be able to use a paddle wheel speedo depending on the age of the MDDC, but mine is a 2000 and doesn't support a paddle wheel input.
Ditto on the "Get Perfect Pass". Do it and you will be much happier with the boat. They can give you a dual function gauge with a tach and speed control for Calabria.