is there another problem with the alternator?
You have gotten one of the early style internal regulators that don't self-excite unless the idiot light circuit is connected. You can either install a 2-wire warning light from the ignition switch output through the bulb to the unused blade terminal on the regulator, or swap to a later-design regulator that has an internal excitation circuit. The newer regulators (sometimes called "1-wire") work as soon as the alternator RPM is goosed up a little after startup.
Jerry
