Hi Mike
The 4 cables are positive, negative, ‘ignition’ light and rev counter. They are (normally) colour coded as follows –
Positive (B+) – Red
Negative (D) – Black
Ignition light (61) – Brown
Rev Counter (W) – Grey
The connectors may give a clue (assuming the new alternator is a direct replacement) as some are rings and one (or maybe 2) are spades.
Good luck
Roger