Our trucks PCM and FCM read a resistance measurement through the headlight and tail light bulb filaments. When a filament blows the resistance drops and this lets the PCM/FCM know a bulb is out and two things happen here.
1) the modules reduce voltage and
2) the Lamp Out on the dash comes on to notify the driver
So because HIDs are gas filled and not a filament type bulb, when you plug them in the PCM/FCM module does not see "bulbs" and those two things stated above happen.
But because the voltage has been reduced, the HID kits will normally strobe or flicker.
The OEM filament type bulbs are 55w/65w bulbs. One the headlight harness plugs there are three wires. There is the low beam (12v), the high beam (12v) and the common (-).
So my taking 50 watt load resistors and adding them onto the HID harnesses, we can used them to replicate the resistance needed to trick the PCM/FCM into thinking there are bulbs there and that will reciprocate the two issues stated above. In other words, full voltage will be supplied and no Lamp Out light on the dash.
Specifically, the resistors get wired as such. We know there are two ends to each resistor and there are three wires on each headlight. Take one load resistor and splice it to the low beam (12v) wire and the other end to the common (-) wire. The other resistor goes with one end spliced to the high beam (12v) wire and the other to the same common (-) wire.
You can find load resistors on ebay. I have pics of mine in my signature links