charging problems

I have a '73 Super and am having trouble with the charging system. A
few weeks ago, the car died on the road and would not restart. The
battery was checked; good. The car did require a jump start,
though. Once it started, it ran fine for a few minutes (idling in a
parking lot), then started idling roughly, at which point the
alternator light came on in the dash. Before the light came on, it
was reading 13.5 volts at the battery. So, I figured it was a
problem with amperage and the alternator. Put a new alternator on;
same problem. Check connections from battery to voltage regulator;
OK. Replace battery connections; problem persists. The only thing
I haven't replaced is the voltage regulator itself. Two questions:
first, I'm told you can test the voltage regulator by jumpering a
certain wire to effectively bypass the regulator. Does anyone know
which wire it is that I'd jumper? Second question, any suggestions
for other possible causes of the problem? Thanks much in advance.