Jumpy volt gauge

Check your bulk head connection for the 2 main power wires going through the fire wall. One is red the other is black, they go to your ammeter in the dash and supply power for everything under the dash. Under the hood the red wire comes from your starter relay and the black comes from the alternator, they both go to the bulk head connector. I just went through this problem with my 70 Dart. Turned out my black wire was very corroded on the interior side of the bulk head connector. I eliminated the bulk head connection for the red and black power wires, crimped, soldered and insulated the connection. My voltage is steady as a rock now! My car starts and runs better! Check out the website "madelectrical.com" he does a good job of showing you how to fix it. Remember this was on my 70 Dart, I'm not sure if your car is exactly the same. You should have the electronic voltage regulator, you have the pre 1970 style in the picture.