ERA Not Charging Properly

[CobERA]

My ERA does not seem to be charging. While driving, the ammeter was most often reading at zero, then occasionally it would jump to +30. Per Bob's suggestion, I removed the plug at the alternator and placed a jumper wire from the socket for the yellow wire with red stripes (third from left looking down on plug) to the socket for the blue wire with green stripes (first on left looking down on plug). I started the car and as I reved it slowly, the ammeter jumped to +30. So, I replaced the voltage regulator, but now it seems to read below zero while driving all the time now. I can't find any loose wires.

Questions:

1 - The voltage regulator that came with the car was an Autolite that said 15V on it. The replacement from NAPA is a 12V model. Does that make a difference?
2 - Is it likely the alternator?
3 - Any easy tests of the alternator?
4 - After I changed the voltage regulator, I noticed that the red ignition switch light stayed on while the car was running. I guess I'm getting to old , but I can't remember if it always stayed on while the car was running. Should the ignition light be on while the car is running?

Thanks,