Backfeed?

[TFagan]

I have installed a 1995 LT1 out of Buick Roadmaster in a 1958 Chevy Truck. I am using the alternator that comes with the engine. I am also using a universal wiring harness for the truck from Speedway (20 circuit) With the battery hooked up, the wire that runs from the 2 wire plug is hot. I believe this is powering up the fuses on that buss bar. I believe they should be getting their power from the accessory wire running from the ignition switch. Even the accessory wire from the fuse panel is hot when I hook up the battery. I am afraid to hook it up to the switch because it already has power. I was thinking it might be a grounding issue - would that cause the backfeed? Any ideas will be helpful
thanks