This opening in the '66-right above the battery-was the perfect place to begin routing the wiring harness. All three legs of the harness pass through on the way to their required locations. The two female plugs connect to the new bulbs, and the male plug connects to one of the original headlight plugs. Run the harness so each female plug comes through the hole in the back of each headlight bucket and the male plug is in the vicinity of an old headlight plug. For the cleanest routing of the new harness, you'll want to use the original passenger-side headlight plug near the relays and fuse. The male plug has already been passed through and will connect to the old one that came off the passenger-side headlight.