Classic/Antique Car Repair: 69 Mustang Mach 1 battery, mustang mach 1, digital voltmeter

Question
QUESTION: I am having a problem with my battery boiling after I drive it. I have completely restored my Mach 1 and have put in two new batteries, a new alternator (42 amp output) and a new voltage regulator but it still not resolved the problem. The car still has it's orginal wiring harness. After I drive it it shows about a 15 volt reading. I did tweak the regulator and thought I had it fixed but after a short drive it is back to 15 + volts.  Any thoughts for how to get this fixed.

ANSWER: The proper voltage regulator setting for you car is between 13.5 volts and 15.3. If the voltage is between these numbers, measured accurately with a digital voltmeter at the battery, then the battery should not boil from charging. But measure the voltage at the battery with a good digital meter. let me know what the voltage is.
Brad

---------- FOLLOW-UP ----------

QUESTION: I took a digital reading after the car is warmed up (but before driving) and it is in the normal range you mention but after driving it the reading is 16+.

Answer
That will make the battery boil. I would suspect that the voltage regulator is the culprit, or there is resistance in the circuit somewhere. Now, do you have an idiot light or an amp meter on the dash. The diagnosis makes a difference. Let me know.
Brad