Can someone explain exactly how the relay wiring harness works. Just a description of install or something. Greatly appreciated. Do i need one for both the lows and the hi's? Thanks

 

Didnt install a relay, but everything im reading is telling me to get a relay harness. I noticed my DRL's run off my hi beams, am i going to hve any issues there? I believe the fogs will just be plug and play! I noticed on website i can buy a relay harness kit that is bulb specific, or a wiring harness with resistors. Or can i just wir in a regular relay harness u can purchase anywhere?