with most 60;s era Ford factory tachs. it states that it will not work with current triggered tachs. If you have a 60;s factory Ford tach in a Mustang or Fairlene it will not work.
I quote "TACH-ADAPT is not compatible with current-triggered tachometers. Such techniques were
used in some older (60's) Ford and Chrysler products that run battery feed to the coil through the vehicle
1968 Ranchero 390. 060 over,10.5:1, Comp 292H Cam, Performer RPM intake, Hooker headers, 4spd. 3.89 dif. ProForm 750 DP, Mallory Unilite distributor, Holley Annihilator cd ignition system, centerforce df clutch.