Four reasons for high charging voltage
1 Bad/ maladjusted regulator
2 Bad ground to regulator and by that I mean the BATTERY NEGATIVE POST is not the same voltage potential as the regulator case
3 Voltage drop on the positive feed from the battery---through the bulkhead--to the ign switch connector--through the switch contacts--back out the ign switch connector--back out the bulkhead connector--and to the IGN terminal on the regulator
4 In rare cases on the newer isolated field systems, either a grounded rotor "in the right spot" or a grounded brush (blame the rebuilders) can cause a "full field" condition.
TO CHECK voltage drop, check the battery, make sure the cells are OK, Run the engine to simulate "low to medium cruise" with all accessories off, then re--test with heater, headlights on
Take your digi meter and stab a probe directly onto the battery negative post, the other probe directly onto the regulator case
On the positive side of things, stab your probe directly onto the battery positive post, the other as close as you can get to the regulator IGN terminal. On 69/ earlier, directly onto the regulator. On 70/ later, probably the blue ign feed to the ballast
IN BOTH CASES you are looking for a really low reading, the lower the better, zero volts would be perfect. Anything over .2V (two TENTHS of a volt is too much) and indicates a problem