Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Hello I will help you with your question,
It is normal for the charging voltage to fluctuate as different loads are applied to the electrical system.
Do you have a picture of the ground you think is missing?
Have you had the battery load tested?
You say a ground is missing? Is that what you mean is you think there should be a wire between the alternator and the battery for ground? The ground path is the metal of the alternator case through the engine to the ground cable that is attached to the engine block.
The electrical system is constantly changing load so the regulator for the alternator changes the output voltage with the load. It is normal for anywhere from 15.5 volts down to 12.6 volts at the output of the alternator. It will reduce voltage to let the alternator spin freely saving fuel when the load is low.
It sounds like your system is operating normally, what is your concern with what you are seeing?