The brown/white wire provides a ground for the idiot light anytime the alternator voltage is below battery voltage, illuminating the light, hence the "L" identification of the terminal on the voltage regulator. One of the terminals on the perimeter of the 10 SI internal regulated alternator serves the same purpose, so if you want the idiot light to function, connect the brown/white wire to the left terminal on the alternator as you look at the back side. The right side terminal gets connected to battery voltage.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!