I had Auto Instruments convert my factory tach to work with electronic ignition. Hooked it up exactly as they said to -- copper/short stuff to the negative side of the coil. Silver/long stud to any keyed fuse. Ran that wire to the radio fuse and it sparked like crazy and blew the fuse, blew the glass even. Put a test light on the wire and lit up immediately. What could be causing it to act as a ground? We tested everything on the back of the tach and everything is acting like a ground??