Picture of the module unit. This module also failed! in this case. When they fail you can get both an under voltage or over voltage issue.
One should check with the help from a Service Tech. or someone with an understanding of alternators to see how to disable the exciter circuit of the alternator.
The reason, You can run many coaches with a generator and a battery charger system on board to keep traveling even if your Alternator fails in regards to its output voltage. This is a good back up plan, just in case there is not a source for a replacement alternator.
If the alternator bearings are still good it will act as a pulley to keep the water pump and other items working just like they should. This will allow you to keep going down the road. I have driven well over 2000 miles this way,to a location where a new replacement can be found!!