Low voltage that points to alternator not charging may be the alternator but don't rule a much less expensive item, the Ignition Switch. The alternator should be charging the battery at about 14 volts or so, Put a DVM right at the 2 terminals on the battery and start the car. Should get 14 volts and should be stable. Turn on the lights and run the AC with blower at highest speed, voltage should drop slightly but not much.
I spent 2 or 3 months shooting a problem point to the DBW TAC on the PCM at the right front wheelwell. Bought another TAC and problem remained, Had low voltage on the control lines. Car cranked but would not run. Someone suggested the Ignition Switch. Finally got the new back or electrical part of the switch (Delco D1499C) and replaced it. BONGO!!! the car started and ran just fine. (If you need a TAC let me know. )

 

 

its all a pain. Check what volts your getting from the back of alternator and at battery.

If its the original alternator it maybe best to try that. Just make sure you get a valeo Alternator for the vette.

 

#1 is do NOT go by the DIC voltage to monitor charging system health...The first thing I'd do is get your battery "load tested" at your friendly auto parts store or if you live in NJ I'll do it for you...LOL !!!...if battery is good are you familiar with voltage drop checking of the charging system ??....if not and you don't have a DVOM you can just remove the B+ terminal at the alternator clean it up (terminal end and stud) and reinstall...do the same thing at the starter solenoid...clean the battery cable and the 2 smaller gauge wires attached to it....and make sure your battery terminals are clean... And yes, you can also have a bad ignition switch,,,I changed mine a few months ago but mine was a "no crank- no start" condition...I knew my battery and charging system were fine (were tested a month earlier)...with key on my DIC voltage was real low...I think it got down to 8 volts or so...no further diagnosis was necessary so a new switch was installed...no further problems. If you have a DVOM and want to attempt the voltage drop check let me know...most of the videos you'll find on YouTube are "almost" correct....charging system should be fully loaded...i.e. high beams on, blower on high, defrosters on...etc...and then test....AC Delco says anything over a .5v drop on the negative and positive side are bad...I like to keep the tolerances a little tighter !!

 

A healthy fully charged battery should be 12,6V give or take. So, after starting the car and having it sit idling you should not be seeing <10V on the volt-meter which is indicating a completely dead battery that would be incapable of even cranking the engine. I would investigate the solenoid connections and the ignition switch for a bad connection that is dropping voltage.