So did you use the stock plug or did you cut the wires and wire them to the plug that came w/ the tach? I tried that, and matched the wires the best I could because some were totally different colors (the first two, I believe) between her wires and the new tach's wires. After I did that, and plugged it in, depressing the hazard lights would make the door ajar "bell" ring.
So then I figured I better stop messing with it.
