Chevycobb

Well I took my car for the first time on the road today after new engine build. Everything sounds/runs awesome but I don't have a tune yet. When I turned everything on for the first time strange things happened. When I turned on the vent my dash lights and radio shut off and my security light came on, but the car was still running and then everything came back on. Then I turned on my fog lights, and my dash lights and radio shut off again but with no security light and my speedo shot up to 110mph and then everything worked fine again...the whole time the car was still running. But it only did that the first time I turned something on, and not again when I turned the same thing on. It was just really weird to me....anyone have any clues?

CSJTA

Check your underhood ground connections, the ones on the passenger side front, sounds like a loose ground