Contact Buddas Marine Electric. Speak with Al. He knows all there is to know about starters and alternators. http://stores.ebay.com/BUDDAS-AUTO-MARINE-ELECTRIC

He can tell you exactly how to troubleshoot, what voltages to look for on which leads, he can do a rebuild for a very good price or sell you a new one (also for a very good price). The man walks on water IMHO.

A few years back I blew my alternator on vacation and contacted him by cell from on the water: He met me in Mystic CT in a parking lot, on a Saturday night, and handed me the new alternator along with his cell number. (The new alternator was a Valeo exact OEM replacement at a fraction of the price Volvo Penta or a marina would have charged). I called him with questions on Sunday morning and he told me exactly what I needed to know and how to measure for proper operation. I could have been delayed until Monday or Tuesday with a thousand dollar marina bill, but I was ready to go by noon on Sunday for around $200. I later sent him my failed alternator and he repaired it for a spare, for a little over $100. How can you beat that? I love that guy.