voltage dropped to 11.5V while driving

[garystocker]

I just picked up a 68 GT Coupe with digital gauges. It was driving well for a couple of days. Digital voltmeter read 14.0 steady.

Now it reads 11.5..

Is it the battery, voltage regulator, or alternator, and how can I tell? They all look newer to me...

 

[garystocker]

guess what it was...loose belt!

 

[James Kirk]

good catch. Most people don't consider that centrifical force produced by engine RPM's can, in effect make a belt "grow". and your voltage probably dropped exponentally with engine RPM increasing.
Kirk