New Alternator?

[Jon4399]

I motored most of the way to my new berth about a month ago. Had no problem with the alternator or electrics. After I left the boat for a couple of weeks, I checked in with Harbourmaster, who told me my engine alarm sounder was going off. They covered it with tape until I returned. On my return, I found the sense wire to the alternator (in the nylon 2-wire plug) had corroded and fallen off. But the sounder and charge lamp continued until I removed the plug. I decided to remove the alternator completely to clean things, and found the unit very hot to the touch. Seems strange since the engine had not run in a month. Any ideas as to why the alternator was getting juice, which to me is the only reason to be hot? Also, I found a Delco 105A replacement on E-Bay. The current engine is a Yanmar 3HM35F, with a 55A alternator. Do I need to replace the alternator, and any thoughts on the Delco?

[captain465]

Take the alternator to an automotive starter/alternator shop and have them test it. I think that it will likely be fine. But I also think that the cause of the alternator being hot to the touch is that your ignition switch may be bad. Alternators need an excitation voltage to operate. That voltage is usually supplied through the ignition switch.

[Blue Stocking]

Could be a faulty, closed relay, if that is how your field current is supplied.

[Jon4399]

Thanks for the feedback. I checked the wiring diagram and there is no relay, other than the starter relay. It seems the only current for the entire system has to come through the ignition switch. I've been leaning towards that being the basic problem. I can't figure any other way for the charge lamp and sounder to be going off with the ignition switch in the "off" position.

[Kettlewell]

Ignitions switches short out a lot, especially if they are exposed in the cockpit. Easy to test by just disconnecting the switch.

By the way, I have my boat set up so I have a master switch that cuts off power to the ignition panel when it is off. Doesn't your master battery switch do that?