Series 1, 2, 3 to GP

I am installing a VAPE 12v AC system on a 1959 Li125. Everything seems to be going well. Headlights work however I do not have 12v festoons for the rear. I am standing at the front of the bike, rev it up and POW the headlight burns out. I try to measure the 12V ac out of the reg and it seems to flicker up to 14+ volts. 2 questions:

1. Is it ok to measure the AC output of the regulator with a digital volt meter set on AC mode?

2. Does the lack of tail light bulbs matter on the overall system load and does wattage of these bulbs make a difference. I am seeing 10w festoon bulbs at my local autoparts store.

Thanks for your input. Feel free to call and chat 407-405-3255

Geo