coil A 1 and 4 out side wire on multi plug to coil use 1N4004 diode
coil B 2 and 3 out side wire on multi plug to coil use 1N4004 diode
these should be incorporated into the wiring on both side of the coil do not cut the wiring as these spur of the loom on there own then join both diodes together using a link wire, then solder the zener diode to this. Zener is 1N532B / 1N5355B 15-18 volt, make sure your green tacho wire is cut from the old loom, the join the zener side of your wiring to this and this should only go to the tacho and no where else. works perfect, do not use the use the wiring supplied from pin 21 on the ecu make sure this is disconnected as the wasted spark driver supplies voltage from this to run your tacho but this doesn't work, see how you get on