Electrical Issues 1975 Dodge Dart Sport

I have a 1975 Dodge Dart Sport with a 5.2 L 318 V8, and am experiencing electrical issues. This morning, I started the car with no problems and I was watching the alternator gauge fluctuating going down and up. I turned the car off and noticed nothing works, the headlights, horn, gauges, brake lights, nothing. When i try to start the car it cranks, but no spark. The only electrical thing that seems to work is the starter and that’s it. Would appreciate any suggestions.