I have a 1991 RX7 convertible. I was out last night and my dash lights would go dim then bright again then dim and I have a buzzing noise now coming through my speakers while listening to my satillite raidio while this happens. What is causing this so I can fix it. It started right out of the blue

 

sounds like you have a short somewhere, i'd start checking your wiring see if you don't have an exposed wiring or loss connection somewhere