Diesel Power,
You start by removing the cover around the switch by pulling on one of the corners towards you. It's held in place with expansion clips. This will give you access to the back of the headlight switch. You will need a t-tap and test light. On 2003 trucks you can tap into the orange wire with white stripe and 2004 & 2005 trucks you tap into the orange wire with a brown stripe. But before you hook everything up, you will want to test it with a test light to make sure it is correct. From there use a t-tap to splice into the wire and run one continuous wire to your lights for your gauges. This way when you turn your lights on, your gauge lights will come on. You can also use your factory dimmer to adjust the lighting of the gauges.