Straight from the directions
Connecting the spark signals.
Locate the EST signal wire. On GM vehicles this wire is almost always white and runs from the ECM/PCM to the coil module. This wire must be cut and spliced unless a plug and play harness has been purchased. If a plug and play hraness has been purchased, install it according to its instructions. Otherwise cut the EST wire (rear most wire on the module harness) with enough slack to be able to strip and crimp (or solder) on the spark pigtail. The white wire of the pigtail goes to the wire that connects to the ECM/PCM. The gray wire goes to the wire that connects to the coil/module. Before crimping or soldering slide a piece of heat shrink tubing over the end of the pigtail wires. Crimp or twist + solder the pigtail wires to the cut ends of the vehicle harness and cover with the shrink tubing. Heat the shrink tubing with a heat gun or a match/lighter (carefully) to seal the splices.
