Perhaps I can make the schematic a little clearer for others, as well.
A relay is a switch that turns on when > 6 volts is appplied and turns off when the voltage drops to < 3.6 vots.
The schematic shows the a common Headlight relay and pin outs as viewed from the bottom of the relay (blades pointed upward).
Connect the 12 volt fused power to pin 30/51.
Pin 87 feeds the power line to the lamps.
Now connect the relay coil (pin 85)to a switched 12volt(+) source and now connect pin 86 to ground.
This is the line that acts as a trigger to close the contacts and complete the off road lights circuit. This line can be run to any 12 volt source and should be fused.
So, as you can see you can switch the relay on, or off, by applying power to the relay or removing it from the relay. So, pins 85 and 86 act as the trigger.
Connect the switch in parallel to the voltage source. This is the third wire from the KC switch. The KC switch that's shown in the schematic is a lighted switch. So there is a ground shown from the switch to provide a ground wire for the lamp inside the switch.