I bought a used Ford Racing Speedcal that was already calibrated for 410's. Its an easy install. All you have to do is cut the stock plug off, pull the 2 prongs out of it, and plug them into the new plug. Anyway I hooked everything up and the speedo didnt work. I pulled it back in the garage, jacked the car up, switched the 2 wires(thinking maybe I had em backwards), and tried again and it still didnt work. There is a little red what looks like a ground strap hooked to the speedcal but the original owner said he never used that. Does anyone have any clue as to what I am doing wrong.