[BruceG1]

When I throttle up my 22'Eastern lobster boat under load my bulkhead mounted warning horn goes off which signals that my 20 amp motor fuse has blown.Ijust installed new wiring harness including key switch and it is still happening .This is frustrating and costly as I am a commercial lobsterman.Any ideas much appreciated.

[MercGuy]

I have pretty much the same engine (1998 Merc 115) and I'm unaware of any warning horn that lets you know of a blown fuse.

Standard warning horns are for high temp, and low oil. Are you sure that one of those aren't your actual problem ?