I also had a bad ground on the frame right below the battery. I cleaned it (dremel) when I installed the new negative battery cable but still had crazy voltage fluctuations and weird electrical gremlins. I ran another ground from the alt bracket to a strut bolt on the tower. Cleared it right up. Took me a long time to figure that one out. I also ran another positive from the alternator to the fuse box post to ensure a good connection.