Some tachometers connect to both primary terminals of the ignition coil, but I don't know specifically about your tach. What did you do with the other tach wire in the twisted pair? The older Sun tachometers used a transmitter under the hood, with two wires going to the tach head, but I don't remember if those were twisted. My first thought is that they were not twisted. The fact that you have a twisted pair going to your instrument leads me to think the pair connects to both sides of the ignition coil. But that is a guess at this point.
Which wire did you have connected to the coil, and which one stopped the engine when you touched it to the coil? And to which terminal did you touch it?
If the tach head, the instrument part, has no electronic circuity inside, it probably needs a transmitter to connect to the igition coil. If you find electronic parts inside the device, those most likely replace the external transmitter, and the two wires in question would connect to the ignition coil. Silver and gold colors might indicate negative and positive- but also a guess.
Harvester
