Wrong Alternator on 1999 SAN GT-40

[Jamo]

A few years ago, before I owned a house and had the space/tools/time to do my own engine maintenance, we had the marina put a new alternator on the boat. We ended up not using the boat for the following season, and since then had 2 years of intermittent boating in the summertime.

We now have a summer place on a lake in NJ and we are using the boat much more frequently. One of the [many] issues I had noticed over the past two years was that my voltmeter was maxed out to the pin. I think this shows something like ~18 volts. We've also gone through three batteries in 2 summers.

I was looking at the alternator last night, and I can't find any markings on it that might give me a clue what model it is. However, I hopped on NautiqueParts and thanks to their good photos, it sure looks like the marina put on the 70 AMP GM Alternator (pictured) which would be incorrect. I think I need to either order the Alternator, Pre 2003 PCM, or do the 100amp upgrade. Both photos are attached.

Does this seem like an accurate diagnosis of the problem? I'm also suspecting I need a new starter, but not sure if that would be connected to this problem or a separate issue.

[NautiqueJeff]

The voltmeter could be bad too. I have one on my '99 that reads about 1.5v higher than actual. I would put a meter on the battery when the engine is running and see what the true voltage is first.

[MLA]

Does this seem like an accurate diagnosis of the problem?

I would not make that leap just yet. An alternator of that generation is going to operate the same, whether its in a GM, Ford or Dinso, etc housing. Its ether an internal or external regulator. Sounds like your current alternator is charging, over charging to be more exact. This might point to a bad cable somewhere, preventing the alternator from seeing any load and regulating accordingly.

Did the batteries die do to over charging or under charging? This will be a huge piece of the whats going on puzzle. The reason for the original alternator replacement, may still be present on the boat.

[Jamo]

I'm assuming they are dying due to overcharging, but I need to check.

I'll need to figure out how to get the boat running on the trailer here this week and then hook a voltmeter up, it sounds like. Curious how a bad cable could result in this--but I suppose I don't know exactly how the alternator should be wired up? I'll do some more digging!

Thanks!

[Nautiquehunter]

I have been using DB marine alternators on my boats for years under $100.00 no problems yet .

[J9015]

The above suggestions are great to pull a voltmeter on it while running. You can also pull out the alternator and take it to an auto store to run a diagnostic.


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