This question was just asked and I've seen it asked a few times before. It's hiding in the manual in the section on the keyless entry, of all places. Pretty hard to find.
With so many members changing over to HIDs I thought this was worth a post. Since they require a heat up/cool down period, it's a great idea to disable the perimeter lighting feature on our trucks.
What is perimeter lighting?
When you press the unlock button with your keyless entry fob, the headlights come on for ~25 seconds. It is used to illuminate the exterior of the vehicle and give better visibility to the user while approaching the vehicle.
Why disable it?
The perimeter lighting feature will, to be blunt, greatly reduce the life of your HIDs. The constant flickering on and off from the perimeter lighting causes unnecessary wear on the bulbs since they don't have time to properly warm up or cool down before their next use.
How to disable it.
Straight from a 2007 Ford F-150 Owner's Guide:
Originally Posted by F150 Manual, pg. 137
Enabling/Disabling the perimeter lighting feature
Your vehicle comes with the perimeter lighting feature enabled. All vehicle doors must be closed before beginning the procedure. You must complete Steps 1-5 withing 30 seconds, or the procedure will have to be repeated. If the procedure needs to be repeated, you must wait a minimum of 30 seconds to begin again.
1. Turn the ignition to the ON position, then press the unlock control three times.
2. Turn the ignition to the OFF/LOCK position, then press the unlock control three times.
3. Turn the ignition to the ON position; the horn will chirp to indicate the driver configuration mode has been activated.
4. Within five seconds, press the unlock control two times.
Note: One horn chirp should be heard, indicating the system has been disabled. Conversely, a horn chirp followed by a honk will indicate the system is enabled. Pressing the power door unlock control two times again will turn the feature ON if it was previously OFF, or OFF if it was previously ON. Every two consecutive presses of the unlock control after successfully entering the configuration mode will change the enable/disable condition of the feature.
5. Turn the ignition to the OFF/LOCK position to exit programming.
Note: After exiting the driver configuration mode, the horn will chirp once to indicate a feature has been activated/deactivated.
Hope this helps some of you guys out! Oh yeah, please readjust your HIDs after installing them. Now that you've readjusted them, aim them a bit further down.