Special Battery Disconnect shuts down the alternator when you flip the switch. This is necessary if you want the engine to shut off at the same time. The 2 extra terminals are wired into your alternator feed wire from the ignition switch. This circuit turns the power off to the alternator preventing engine run on when the switch is turned off when / if the engine was running. Rubber stud boots included for large terminals.
Note: You do not need this switch if you have a "One-Wire" Alternator, as you do not have the second wire that would attach to these terminals. Just use the MS-1.