If you look at the picture on the zip file, not in the document, you are powering up what is essentially the high beam circuit, which is why with my mod, if you have the parking lights on, and you push the high beam switch forward, the highs will turn on, which normally only works when the low-beams are turned on. The diode prevents your low-beams from turning on when you turn your switch to parking lights. The reason the power has to be fed to the high beam relay is because that is the only way I've found, besides modding the whole switch assembly (which I haven't gotten to play around with yet) to have the parking light mod while still retaining factory functionality of the fog's turning off when the high beams are turned on...