Car is overcharging. Please help!!

My car is overcharging its reading 16 volts at idle and 18 when i give it some throttle. I have a 2 wire alternator and it looks fairly new i got it from one of my buddies because we thought minds was bad. Voltage regulator is new also i have tried to check grounds but i cant see anywhere that may be grounding out or not grounded at all so it is really frustrating me. When i first start car and take off car is driving fine but after a few seconds or minutes when i come to stop i hear a popping noise coming from exhaust and when i pull off it breaks up real bad. So i trying to distinguish if im getting to much gas the reason why it does that or is it a fire problem im using an electric fuel pump and regulator. I also have a brown lookin wire coming from starter relay that i dont have a clue to where it goes due to car had no motor or trans in it when i bought it. On the voltage regulator does both sides need to be grounded cause i only have one side that has a screw in it due to the place that i could put it on the firewall where the old style regulator was or do i need to move it. Can someone please help me fix this or these problems because they have me stomped. Thanks alot.