As you have a zetec you need twin coil, single coil means the conventional(old) set up with a distributor and a cylindrical type coil, whereas your zetec uses a coil pack which is effectively 2 coils in one, using wasted spark.
The rev limiter connects into the three pin plug connection, usually earthing out the negative wires momentarily which pulse each side of the coil, for cylinders 1+4 and 2+3 to effect no spark, no over rev.
tabetha