low/no charging

Somehow I'm still not getting through to you. .......................Your alternator is NOT factory...........the box mounted on the alternator is surely the VR....................a photo of that box would tell the story.

THIS is a powermaster and likely what you have.............This one is similar. It's just a "little box" which the wires on your alternator hook to.........

So far as testing yours, and since you cannot find the starter relay, you are in reality looking for a battery source. That terminal you pointed to in your photo is where you can hook the second field terminal. Do NOT leave this hooked up any longer than necessary to see if it's charging