Pulling the battery lead off with the engine running might have been OK for your dads 67 chevy, but it is extremely risky for a modern car. An unregulated alternator can put out over 40 volts at idle, A shorted diode can cause an opposite polarity spike. This can damage your electronics.
A voltage test with all the accessories on is the best way to test. And as Ray said, raising the RPM under load and testing the voltage is important.
jeff
