[Lynn Eades]

Svenn, if you drop the belt off, and then supply power to the big terminal, the genny should run as an electric motor. If it will do this, I would clean the contacts in the regulator.
"Motoring" the generator, is a quick way to check it's overall condition. If it won't "motor", then it needs work. If it does, then it's likely the regulator.
A quick way to check if anything is happening is to turn on the headlights. if you then start the engine, with a few revs on, the lights are generally are brighter, because the voltage has risen above battery voltage.