Might need a separate wire harness that plugs into your alt and connects to your factory harness. The same thing happened to me when I bought my singer alt. I contacted mike and told him what was happening and he said that was a common problem because the high output alt trips up the cars electrical system (or something along those lines) and could make your volts rise and drop quickly and drastically so I needed a separate wire harness/adapter to keep my volts at a constant number and its been all good since, don't drop below 14v. Mike had said its a common occurrence on some vehicles when you put a HO alt on. That might not even be the issue though just thought I'd let you know what happened with me just in case. The harness was only like $20 bucks by the way