I have one of those early small tachometers that mounted in the late 70s/early 80s instrument clusters. I want to test it on the coil of my '91. Seems like it would be easy - jumper wire to 12V power, jumper wire to ground, and coil input wire right to the coil. Could I do damage to either my vehicle or the tach by doing this?

Also, the coil has two male outputs, one labeled +15 and the other -1. I assume I'd attach the coil wire to the -1 output, as the white/red wire that feeds my large cluster mounted tach is attached there. Plus, the back of the small tach has a (-) sign by the coil input.

Thanks-