I am new owner / slave of a sailboat, 1984 hull#329 MKI. After a cruise in July I was going to replace the alternator belt on my M25. As I loosen the alternator, it fell to the sole. Yep, I had to replace the alternator mounts with the upgrade kit. 
Now that it it back together I find a blown 30 amp fuse at the bulge pump switch. I replaced the fuse. The pump doesn’t work. The temp gauge is pegged and the tach no longer works. I can only assume the the alternator shorted against the engine block as it fell. I figure I will have to replace the gauge. My question is, how do repair the tach. Is there a part I can change on the alternator? Do I have to buy another?
Thanks.