When installing HID lights in a 2001 or 2002 Toyota 4Runner (Bi-Xenon H4 HID Kit), you need to disable the Daytime Running Lights because the DRL circuit lowers the voltage to the stock halogen light bulb to create the DRL effect.
When installing HID's, if your truck sends the 6v signal to the headlights for DRL, it will upset the new HID ballast, and the xenon bulb will flicker like a strobe light. Disable the DRL circuit to fix the issue. The following write-up will show you how to disable it temporarily with a switch. If you install HID lights and do not plan to take them out of the truck, then the switch is unnecessary. Disable the circuit and forgo the switch installation.