I think the reg is bad but first unplug the field terminals at the reg & confirm that neither male alt terminal is grounded & you might note how many ohms there is on that circuit & there is a spec for that & you spin the pulley by hand which woouldn't involve anymore than removing the belt for a quick test tho likely if the brushes & that circuit ain't grounded then the alt is good but it would be a good first step (& costs nothing). Do NOT run the eng any longer than 5 seconds at a time just long enough to take a voltage reading with your VOM as you proceed with the diagnosing & keep all lights/accessories/radios etc off even for that 5 seconds.