Wiring Lights Using Relay - 1. The connection shown in photo A supplies the control power to the two relays in the new harness. Just plug one of the stock (faded yellow) headlight connectors (female H4) into the (bright yellow) mating connector (male H4) on the new harness.. Please read this introduction! There have been significant changes to this particular web page! There are several sections in this website that you should read regarding track wiring..