What amount of voltage should be at the battery terminals when car is running?
 

Just replaced my battery on my 66 GTO 389 4 speed. What voltage should I be reading at the terminals with the car running? Also how do I check the voltage regulator and alternator for correct voltage output?
Thanks,
Fred

I'm sure you'll get a lot of difference answers, but you should be in the neighborhood of around 13.8 volts with the car running. If you're down in the low 12's or nearing 15 volts or higher, you probably have alternator or regulator issues.

Mine is reading over 15 volts with the engine running. How can I check the regulator and alternater. Is the voltage regulator built into the alternator?
Thanks,
Fred

On a stock 66 the voltage regulator (Delco-Remy) is mounted on the firewall.

OK guys thanks for the input. I disconnected the leads going into the voltage regulator and plugged them back in moving them around. Now I'm getting 13.5 volts with the car running and the headlights and blower motor on. Guess I had a bad connection at the voltage regulator.
Thanks,
Fred

If I recall correctly, the external regulator should limit the voltage to about 14.5 volts. That's one of the reasons that if the battery goes bad, the charging system can't "force" a charge into the battery - the voltage limit.

Check6, clean the trerminals and the plug side then use a bit of dielectric grease on the terminals so the don't corrode.