See this 57 colored wiring diagram: https://www.trifive.com/images/1957 chev wiring color (2).pdf

You must have a repo regulator....There was no #4 terminal on the original:https://www.muttonhollowchevys.com/1955-1956-1957-Chevy-Voltage-Regulator_p_968.html

 

Helping a friend out that just bought a project car. It's charging OK.
And it probably has a regulator off another older chevy. The alternator on it is for external regulator. Just baffled about where the wire on the #4 connects in the harness. Maybe for a light in the dash?

 

A part number or/and pic of the regulator would help

Check out the attached article:

Also see:

 

Photos of regulator

 

As Davids diagram shows, #4 goes to the "gen" light and is a brown wire in a stock front light harness. You don't have to have the resistor shown. That's a back-up ignitor if the bulb burns out. That's a externally regulated alternator regulator.