New Regulator ?s

I have some questions about voltage and regulators. I had to buy a new voltage regulator today. The old one started cutting out most of the time, but would work enough I was able to keep driving the car. Before it started going out I noticed that my volt gauge would read 15 volts for a while after I first cranked the car but would drop down to just below 14 (13.8's perfect, right?). Now that I replaced the regulator, I crank the car and the factory alt gauge surges up to the 3/4 mark then slowly drops to just above the 1/2 mark (never did that before) and my volt gauge is reading a steady constant 15 volts. I've read other posts on the forum of people smelling wires burning at 16 volts.
My question is, does it sound like the regulator is faulty and what are the tolerances as far as voltage is concerned. What's too much? At what point do I shut the car down to avoid frying wires?

I HATE wiring problems:banghead: