Pull the panel below the steering column. Look up at the column and you will see 4 wires with labels on them. These are the wires for the upfitter switches. I believe that switches from left to right are fused in the following order: 30amp, 30amp, 10amp, 10amp
Use the end of these wires to supply power to the accessory your adding. The switches are fused and powered from the factory.
Go to the following link for your high idle mod. It's listed for and '03, but it worked fine on my '05, and will probably work for your '06