fresh 318 questions

OK, get the engine running at a fast enough idle that it shows charge on the meter. Unhook first one field wire, and see if the stops charging. Then unhook the other and see if it stops. This will confirm that the field circuit has control of the system.

Next, hook up "as normal" and check the regulator ground. To do that, put your meter on low DC volts, and with the engine running at a fast idle, stab one probe onto the battery NEG post, and the other probe onto the mounting flange of the regulator. Stab through any rust, chrome, paint. You are hoping for a very low reading, not over .2V (two TENTHS of one volt) More shows the regulator is not truely grounded

I assume you are using the isolated field/ 70/later system?

Turn key to "run" but with engine off. Put one meter probe on the blue field wire connector, the other probe on the battery positive post. You are hoping for a VERY low reading, only a few tenths of a volt. I you see more than .3V or worse, you have voltage drop in the ignition harness which will cause overcharge

If the above tests show OK, replace the regulator