Well in the case of the oh so common GM delco "1 wire" alt the hot rudders special.
There are actually 3 connections.
One heavy stud terminal goes to the battery [usually via the starter to save wire]
Then the 2 spade connectors with lighter gauge wire are for the charging light and regulator sensor wire.
The indicator light is grounded through the alternator.
There are options for the regulator voltage sens line.
They're called a "1 wire" because the indicator light terminal does not need to be connected and the reg sens line can simply be looped to the heavy output terminal of the alternator.... now IDEALLY the reg sens wire should go directly to the battery, so the battery itself gets the correct voltage regardless of poor connections between it and the alternator.
Not sure if you have that alternator, they're quite common, but what it comes down to is typically you have a heavy charge current carrying wire direct to the battery.
A lighter gauge wire connected directly to the battery for voltage regulator.
And another lighter gauge wire that goes to ignition to "turn on" the alternator.
[The gm delco are "self exciting" so the "turn on" wire is omitted.
Hope I didnt confuse things [I feel like a confused myself there..]
And this is very typical unless you looking at a Chrysler that has a "generator" instead of a alternator.... which just means the regulator is remotely mounted....I doubt your massey woukd have that though.Screenshot_20190414-212729_Chrome_1555298866080.jpg