important if the boat was using the stock internally regulated alternator. It was the same set up on my Volvo. With the new, externally regulated "smart regulators" it's not the case. It would be important on Al's old internally regulated alternator which had been modified for use with his (now replaced) Automac . That's because it used the internal regulator unless he was applying voltage to the field winding with the Automac's rheostat. The Automac just added a second source of 12V positive that could be adjusted but didn't do away with the internal regulator as is what happens with the new style electronic smart regulators. When Al was charged up, he was running just like his system was standard, right from the factory so he would have needed the light in the circuit. When he was sitting at anchor he dialed up on the Automac what ever voltage he needed to excite the alternator above and beyond what the internal regulator would do to achieve an alternator out put that would charge at his desired rate. The new regulators have all that built in and does all the charging for you in three steps.