Do you have a maintenance man taking care of your equipment, or do you try and fix every thing yourself?
If you don't get that alternator tested, at a shop, or with a volt meter, which can cost 5 o 10 bucks, you might compound your problems. Those regulators are not cheap.
That alternator could be a one wire alternator, using a built in regulator, or external regulator, or an alternator feeding ac voltage to a rectifier/regulator. You have to know these things to properly diagnose the situation.
A hydraulic gage, and a volt meter are things one should have with a machine like a PT. An amp meter is also useful, and a good volt -amp-ohms meter will check current up to about 10 amps.