Charging issue

My alternator in park and while driving seems to have a good charge at 14.05 volts. But while at a light in drive it drops to 12 volts and if I have my fan on or headlights on it drops to about 10.5 volts. I have a stock style distributor with a pertronix set up in it and a msd digital 6 box and blaster ss coil.
Now I've been looking at other posts and saw a way to check for issues such as hooking a voltmeter probe to the pos side battery post and the other probe to the ign side of the voltage regulator. They say anything over .2 volts is cause for concern, mine reads .66!! Then the other test was with the car running hook one probe to neg battery post and the other probe to the voltage regulator case. Again they say anything over .2 is bad, mine reads -.05!?! Why would it be negative? And how can I fix this problem since it clearly seems to be my issue. Thanks a lot for any help! -kory