Probably a remote sensor for voltage regulation and the warning light. With any luck the remote sensor wire can be used to reduce alternator output by increasing the voltage to it to shut down the alternator or at least connect it closer to the alternator output giving it a higher voltage than the loaded side of the battery positive terminal with the line drop from the alternator power wire run.
sounds great but have you ever seen flying belts?? and the poor regulator if external would go crazy with field current trying to output some voltage when the belt was off. Internal regulator would not be a problem as they operate off the generated voltage inside the alternator.