Thanks for your help on this one Lakeside, Rambling Wreck, 2000epic and wakejunky.
Turned out to be a connection issue. One of the wires was pinched (for lack of a better word), wearing through the insulating cover and into the wire-which then corroded. Took me a weekend to find it and had to clean out my bilge to do it, but boat runs smooth and the bilge has never been cleaner.
thanks again