Ditto to all of the above. A 6V system simply won't tolerate a loose, dirty, or high resistance connection anywhere- - - -there just isn't enough voltage to push the current past the resistance. That's the primary reason manufacturers switched to 12 volt systems- - -they're more tolerant of less-than-perfect connections and smaller gauge wiring can be used.
When measuring terminal voltage at the battery posts it's vital to have a fully-charged battery. A low battery will give a false reading as the voltage will continue to rise as the battery comes up to full charge. If the terminal voltage is less than 7.5 volts with the specific gravity of the battery acid above 1.265, you need to SLIGHTLY increase the spring tension on the set of regulator points behind the "F" terminal under the regulator cover. A tiny change makes a big difference, so don't overdo it. Good luck, and keep us in the loop!
Jerry
Edit: Pulling a cable with the engine running is an old shade tree mechanic trick used by folks who don't understand how to check things using meters. A generator can tolerate the abuse, but NEVER EVER DO IT with an alternator equipped system. The resulting voltage spikes can destroy the diodes in the alternator, as well as any other solid-state devices in the electrical system. I have seen voltage spikes go to above 100V on an oscilloscope attached to the charging system when that's done.
Jerry
