Help!!! Charging system 1995 (or 94) E225stler

The tach and charging system would work most of the time, When they quit all I had to do was hit a wake and the jar would start them back. I put a new humminbird 797 on the boat with a voltage read out, and it showed only 11.5 to 12.2 volts when running 5500 rpm. This weekend complete failure of the charging system and tach. Whats first ? Thanks for any help.

If you got lucky, remove the wing nuts and replace them with nylon lock nuts and washers and hope for the best.