This past winters project was complete mechanical, electrical and hydraulic rebuild of my 1971 XKE. As often happens with these vintage cars the wiring harness had been cobbled numerous times. Used the experience of forum members to hook up with British Wiring out of Chicago to purchase a complete new wiring harness. When installing, I realized that no wiring diagram shows the schematic for the ballast resistor harness. This link will provide the missing diagram and narrative. https://www.xke-lovers.com/ballast.htm