My 84 automatic vette has some charging issues since the beggining when I purchased it over a year ago. When I first bought it I noticed that the battery volt meter reads 14.4v when driving and when at a red light the volts drops down to 11v or sometimes down to 9v depends how long the red light is. So I figured it was the battery so I purchased a generic brand battery. Still the same thing. I then bought a generic brand alternator from Canadian tire and put it in and checking all the connectors and cleaning them and still had the same issues. This is during the day time when theres no headlights on. It was pissing me off so bad, I ended taking it to GM to get it serviced and they say that the alternator is faulty and I needed a new one. So I bought a OEM Alternator from GM and told them to change the battery to a AC Delco. The drive home it stayed at the 14v range and the next day it was back to normal with volts dropping. Later that night I drove around the city I noticed that my headlights were getting very dim and them the engine shut off becuase there was not enough voltage. Got a budy to boost me for about 10 minutes and it gave me just enough power to get home with no headlights on. I took it back to GM and they are not sure why it is doing this. They did testing and they say it appears to be charging and they re cleaned the contacts. Also checked to see if there was anything draining the power while the car is off and nothing. I am all ticked off becuase I spent more money and it did nothing. Bassically I put the car on the charger all night then drive it the next day. It gives me enought power to run all day becuase its a new solid battery. I can say that the battery does get some charge from the alternator but not enought to keep it running. Also I do not have any big fancy stereo that will juice the power down. Can someone help please!! Thanks in advance.

 

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The voltage regulator in the alternator attempts to keep constant voltage across the battery. The alternator is designed to put out 14.7 volts cold and its output voltage drops to 13.7 volts hot, this is normal. Dash voltmeters read 0.3 volts low because they measure voltage after the ignition switch contacts which have about 0.3 volts drop across them. If the alternator output voltage is below 13 volts or above 16 volts, the red battery symbol will light on your dash. In your case with low battery voltage, the light tells you that the alternator is not charging the battery. When you have low battery voltage (below 13 volts), engine running, measure the voltage across the battery terminals and from ground to the output terminal on the alternator. The voltage should be identical. If the alternator output is 13.7-14.7 and the battery is significantly lower(less than 13v), you may have a defective fusible link in the output wire on the alternator which works ok cold but becomes resistive hot, or a loose nut on the starter motor which is where the alternator output wire goes to. Engine off, measure the resistance from the battery positive terminal to the alternator output terminal, your ohmeter should read the same as touching the ohmeter probes together. Next, unplug the connector on your alternator and look to see if the connector pins are clean and have some spring to make reliable connections to the pins on the alternator.

 

Thanks for the reply. I doubled check all the wiring and it is all good. Also just got the starter replaced and the bolts are on good. I dont know where else to start? I was thinking replacing all the the main elecltrical cables such as the positive and negitave terminals, Alternator cables and starter cables. I hope that would help or no? I just hate putting the car on trickle charger everynight. Im also suprised that an authorized corvetter dealer cant even figured this out.

 

Try changing the positive and negativ cables from the battrey to the starter. Then check to ground strap for corossion and breaks. I got this suggestion from my father in law who was a mechanic in the army for over 20 years.

 

When the voltage drops below 13 volts, is the battery symbol light on? What voltage did you measure on the output terminal on the alternator, engine idling?
Did you measure the resistance from the positive battery terminal to the alternator output terminal? What resistance did your meter measure?
With the low voltage you see, your alternator clearly is not charging the battery, your car is running off the battery and it should be running off the alternator.

 

I am not the best guy to ask when it comes to that but I had an authorized GM/Vette dealer checked it out after I dropped a bunch of $ into it. They say that the alternator is fine and its charging. There is something not wokring properly obviously

 

I had the same problem with my 84 about 12 years ago. It turned out to be the connection to the starter. Check it out. I had it serviced at a Chevy dealer and they said they had seen the same problem on several other c4s.

 

There are two other checks you can make. First check all of the alternator connections on the alternator bracket, especially where it connects to the engine. Another item to check is the serpentine belt. If it is old and worn it will have a tendency to slip.