I followed the instructions from SLEE offroad (google search).
Get the switch from Ian Rubie on here, he usually stocks them and you'll save lots rather than going to a main dealer.
You also want to do the pin mod if you want to disable automatic selection of CDL when in low range.
If you have an Auto you will probably find that pulling the plug off the transfer case will work better for you than the pin 7 mod.
The Pin 7 mod will give you full manual control over the centre diff lock however you can achieve the same thing by pulling out one of the plugs a the back of the transfer case and you get the added advantage of smoother gear changes in low range with the auto.
If you lie under the truck looking forward you will see two connectors at the back/top of the transfer case, one at around 12 o'clock and the other at around 1 o'clock - unplug the one at 1 o'clock and seal both ends of the wiring.
(It's also a lot easier to do than struggling upside down in the drivers footwell trying to get the right pin to disconnect )
Julian, that's what I did. OK, I had a look at the pin mod and it's no nightmare, but the unplugging option is a breeze and as you say works and absolute treat. The low range gear ratios / changes are terrible. Had to unplug a couple of leads before I found the right one though