Have you ever tried to run a welder, air compressor, or battery charger plugged into a long extension cord? It doesn’t work very well. The reason it doesn’t work well is due to the length of the wire connecting the tool to the power source. Using a long wire (or extension cord, in this case) means increased electrical resistance, which means not enough power to get the job done. If you own an older truck (built before 1998), you probably have a long series of wires that stretch from the battery to the fuse box to the headlight switch on the dash, and then back to the headlights. By adding a relay, you effectively create a shortcut for the electricity. This means more power for your headlights, because of the decrease in wire length (and resistance). In our case, the battery was less than 1 foot away from the headlights, so adding relays made perfect sense.