1994 Camaro Z28 Electrical Problem

Do you have any anything special installed, such as an amp or any engine mods?

Where did you buy your alternator and what brand is it?

Have you had it's output tested with a voltmeter?

Alternators for domestic cars are not exactly the most well-built components. I've known many people to buy rebuilt or new alternators that couldn't provide stable output, and they had to be exchanged, sometimes multiple times.

Does anything other than stopping seem to set it off? Try turning everything off in the car to see if it still occurs.

It may be that your cooling fans engage and draw too much current from the system once you're stopped. I'd take a look at them for sure. Try idling and turning on your lights, as well as either your AC or Defrost, since it engages the AC pump and fans as well, to ensure the AC doesn't lock up during the parts of the year when it's not needed.

If your voltage drops when the fans engage, I would have them and their wiring inspected.

Just a quick and easy check for the simple fact mine was kinda doing the same thing just out of curiosity I grabbed pigtail that plugs up on the alternater and I could wiggle it quite freely so I went to napa got a new pigtail it fit very snug I never seen the volt gauge drop anymore that plug is right by the manifold just a thought and good luck