The isolated ground alternators usually have a piece of black plastic under the mounting stud. It is quite easy to visually separate the isolated ones from the non-isolated ones.
I was thinking that maybe we should have a file section ,where owners could list facts or lessons they have learned ,where they could pass them on so that other owners do not make the same mistakes . An owner could go down the list ,read them and learn from other's mistakes.
To that end ,I thought I would pass on something I just learned ,that many of you probably already know ,but perhaps not all.
I have been losing zincs , for years at an accelerated rate , so I have always replaced my zincs religiously . I have made attempts to find the cause ,asked a electrical mechanic assess the problem ,then it would fall off my radar for awhile.
This week ,upon Bill's advise I purchase a voltage meter ,not one with a light ,but a digital one that showed voltage. I connected the pig tail to the quadrant/zinc and contacted the probe to the positive and neg. battery terminals. It showed nothing on the neg. terminal ,but it showed voltage on the positive terminal on both my 24v and 12 v . That meant that I had a negative leak on both the 12v and 24v side.
I had a couple of conversations with Bill ,and I thank him for his time, we trouble shot the issue and possible causes. I concentrated my search mostly in the engine room and in a couple of hours I discovered what my two issues were.
The 12v side was the result of a previous owner having connected a neg. wire from the starter to the fuel pump shut off ,this should be run thru a relay ,I need to look at another SM with a Volvo TMD22A to see how to wire it. That was unique to my boat. The 24v. side is a mistake that I want to pass on ,so others don't make the same mistake.
I disconnected the 24v ground wire off my alternator and found that I had continuity between the terminal and the alternator case,which means continuity between the terminal and the bonding system since the engine is bonded. Once disconnected ,the 24v leak was gone .
This is the lesson I learned : I did not realize that alternator terminals are not necessarily isolated ,more often they are not ,as it does not matter on most boats. So if you purchase an alternator ,make sure it has an isolated ground and if you have a neg. leak ,check to see if your alternator may be the problem.
Hope this helps,
Sassafras River, Md.