I guess I'm the (unofficial) generator expert on the board (challenges willingly accepted, but understand I'm an old curmudgeon).† 30 years old? Hmmm.† Kohler?† Hmmmm.
They built some fine generators back then.† How about you send me a Model #, Spec # and Serial # and we'll see if I can help you out.
Is it gas, LP or diesel?
My first guess, inasmuch as there is no circuit breaker to protect the generator, is that the Voltage Regulator is history.† That's sort of a protective measure generators use to keep people for burning them up.
Feel free to send me the info 'off board' and I'll do my best to help you straighten out your dilemma.
If it is 30 years old, there is a good possibility it has brushes and slip rings. If so, make sure the brushes are free in their holders and the slip rings are not corroded.
The next thing to do is flash the field. Generally can do this by applying 120 volts momentarily to the output leads, although this is not the preferred method.
An even older curmudgeon.