You can attach the purple wire to the negative side of coil crimp on the spade connector. (not the spark plug wire) If you are not sure which is the negative lead, try one, if incorrect no damage will occur. When testing, if unit fails to operate simultaneously, simply move the wire to the other coil lead.
Alternately this can be connected to a Hot Pink wire the tachometer signal is best. This hot pink wire covered with a black boot about 1” long under the dash on the tank or behind the headlight or in a harness under the seat.