X2 Wire should be in place. It is 60" long, 1.4 ohm resistance. Connected to the run side of ignition switch lowering voltage for the stock coil. If by chance it has been removed, a 1.4 ohm ballast resistor can be wired in. Here is a pic of the wire and schematic for a 66, but it'll be the same. Wire #16a, color pink.
66 Coupe 200ci I6 Stock
66 Bronco half cab 203ci I6, CI aluminum Head and intake, Holley 390cfm 4V, Clifford header, Isky cam, KB pistons 9.7:1 comp, DSII ignition