Not charging with headlights on

One way to test the voltage regulator is to use a voltmeter. With the engine running first test for ground at the regulator, this is done by measuring the voltages with the black lead on battery (-), to regulator case. If voltage is near zero good. Ground is very important, it happens via mounting screws. It is also good to check voltage at engine, body, and alternator case to insure they are all grounded, this means when measuring between them, the voltage is near zero. The test continues below.

Since the alternator and regulator have been upgraded, there is uncertainty in the wiring, since the wiring is different from the original. That you call dual field is really, single field with two connections. The early alternators connected one to the case, the other was driven by regulator. The newer brings both terminals out, one is the powered when ignition is on, the other is pulled to ground to complete circuit by regulator as necessary to regulate. The original powered the single field wire via regulator fron (IGN), again wiring is different. Searching topic and wiring diagrams may help.

The regulator has three connections, ground (case), IGN (Blue), and FLD (green). The (IGN) Blue wire voltage should measure about 13.8V with engine running, and the battery voltage should read very close to that too. If the battery voltage is higher by more than a few tenths there is likely connection problems at bulkhead terminals. By searching this form there are countless posts on the problem, trouble shooting and fixing related problem.