Hey guys, I hate to ask the same question twice, did a search and did not find an answer. So here goes my stupid question for the day.

Should there be a ground wire from the alternator to the body? I have a '69 big block with the stock alternator. The alternator has a post on the back for a ground wire but obviously no wire is connected and everything works fine.

Thoughts? Thanks.

I've seen lotsa alternators with a ground post on the back, not a one with anything on it.

The Alternator is grounded already via the bracket to the engine block. My guess is the ground terminal is there as an extra source in case the body ground is not sufficient enough in certain applications.

You need some kind of good electrical connection between the battery negative terminal or the engine to the body of the car. Some have a wire off of the battery negative terminal to the fender while others have this and a flat braided type wire from the back of the engine to the firewall. Whether you use this threaded hole on the alternator to the body of the car or do it a different way you do need to tie the body of the car to the rest of the cars electrical system.
Anytime I put on a high output alternator on customer's cars I use the threaded hole in the alternator case for a ground to go between it and the battery as I am also running a new larger wire from the output post of the alternator to the positive post on the battery and I can run them together over to the battery. Since a stock alternator and the factory wiring is designed to use a minimum wire size anytime you upgrade to a higher output source you also need to upgrade the ground connections. It all has to work as a looped type system. If you have an alternator or an amplifier in a vehicle most people run a big enough power wire but a lot of time fail to address the return path (the grounds). If a ground path is insuffecient this becomes a choke and will not allow the electrical device to work properly.
Jim