I bought this tach on fleabay about a year ago and now it’s time to hook it up. It was advertised as a 6 cylinder marine tach. So I thought it would be perfect for my single seat project running a Dodge flathead six. I stuck it in the dash and ran my wire from the coil to it, once I touched the bottom bolt on the backside of the tach it grounded the coil and the motor died. Is this a tach that needs the box to go with it? Any help would be appreciated.