What Relay do.
Normaly when you turn on light there is a relay in car's original wiring to save the weak wiring of your switch or others.
What electrition do is.
put 2 relay for low and high beam.
When wiring relay They take one wire and connect that into ground.
Other wire coming from ur switch will power up the relay only. so that needs small amount of current now so ur switch is also no longer under load of heavy current flowing across small wiring.
One wire will come from the battery direct from positive and one will go the light .
As soon as you turn on the light the relay cicruit powers up and the point in the relay magnetizes and sticks to the other point that completes circuit of your light and direct battery and bcoz of direct current u will feel improvement of almost 40% in old cars. New cars got relay installed or with newer wiring in them so no need for that now.
I was sick of the electritions installing these relay but now when i understand its not a bad thing u kno. and its no Rocket Sci.