Apparently your alternator is not active or functional. Some of the single wire alternators have to reach a certain RPM before they activate, I think something like 1500RPM or so. Rev up your engine and see if the volts go up to 14 or so. If not I would suspect a defective alternator. Just to double check get a voltmeter and test voltage directly at the alternator hot post with the engine running above 1500RPM. If that doesn't get you at or above 14V then the problem is the alternator IMHO
If there is 14V at the alternator but not at your dash voltmeter then there is a glitch in the wiring setup from the new alternator to your main 12V harness - bad link, relay off, fuse etc. Good luck, let us know what you find!