Bought a 93 Deville and trying to get it on the road. It hasn't been used for years and I was told it needed a fuel pump. Decided to test relays etc first before dropping the tank. Checked full pump fuse under dash and swapped its relay with another. When I turned on the key it blew a main fuse or something and everything went black. I removed the relays again and they all tested out fine? Any opinions on how to test for a bad fuel pump? What could I have blown?