The pull down **** is a bypass for the vacuum. The vacuum applied to the headlight relay(s) holds the diaphram in the up position which prevents vacuum from being applied to the headlight actuators. When the headlight switch is pulled it should allow for air to be pulled into the system which allows the daiphram to relax and the plunger in the relay to drop, allowing vacuum to be applied to the actuators, raising the headlights. The bypass **** also allows air to enter the system and relax the diaphram, effectively acting as the headlight switch does. The bypass switch is nothing more than a plastic block moving inside a plastic body. Moving it downard allows air to be sucked into the system.