There's several possibilities
First, what kind of work did this shop do?
Second, why did you change the alternator/ regulator, because of this problem, or other reasons.
So first, do this:
Identify the green wire hooked to one of the alternator field connections (one should have blue, one green, hooked to the two push on terminals of the alternator
Unhook the green, start the car, see if it charges. If not, OK
If so, the problem is right in the alternator, one brush is grounded and should not be.
If it stopped charging with the green unhooked, now hook it back up, go up to the regulator and unhook the connector at the regulator. If it stops charging, OK
If not, you have a short in the harness in the field circuit
If it stopped charging in either case, now do this:
Turn the key to run, engine off. Hook your voltmeter, one probe to the battery positive, other probe to the blue wire on the alternator. You are looking for a VERY low reading, the lower the better. Over 1/2 volt is way too much, and it should be less
Now check the regulator ground. Start the car and run at a low idle with the voltage not over 15, if possible, by adjusting the idle speed.
Put one meter probe directly onto the battery negative post, and the other directly onto the regulator case. Be sure to "stab" through any rust/ chrome/ paint on the regulator
Here, you are looking for a VERY low reading, the lower the better, zero would be perfect. Anything over .2V (two tenths of a volt) shows you have a ground problem between the regulator case and the battery
IF the above all checks out, you still have a bad regulator. "New," by the way, does not mean "good."
