Well, I am surprised by the lack of guesses or advice.
I went to the boat yesterday and started a visual, based upon what didn't work.
1 - I knew I had blown two 20A fuses - so something was shorted out
2 - I knew the tach was not working
Looking at the tach sensor, there are two wires going to it, and one had been knocked loose and was laying against the metal part of the block. Yes, sa ys he, that could cause a fuse to blow.
I squeezed the terminal a bit, re-attached it, secured it in place with "Rescue Tape", replaced the fuse and all is well.
Tach works, buzzer buzzes, instrument lights light up and the alternator alternates!
Always learning something.
Irwin Citation 34