Used jumper wire with correct ends for doubling back on the tachometer leads from the under dash harness. Works for all generations 1967-68, 1969-70, and 1971-73 Ford anything and Mercury, and Mercury Cougar with factory tachometers. If your tachometer goes bad, you will not start or keep your engine running. Good for bypassing tachometers for testing and getting home. Keep in your glove compartment or tool box. Mostly the wire color is red, but sometimes there will be other colors.