Tools:
Soldering Iron / Solder
Heat shrink tubing
Mini Sub Slider Switch (SPDT type, not momentary type)
3M 558 Connectors or equivalent (T-taps, self-splicing taps, etc)
Fully Insulated Male/Female Quick Disconnects (or equivalent)
Stripping/Crimping Tool
Correct resistors and or variable resistor needed for your passlock system
Some extra wire
Steps:
Remove the center air outlet with two small flat headed screw drivers (1)
Remove Radio and Intrument panel if needed.
Tin the pins on the mini sub slider switch.
Strip and tin 3 short lengths of wire and solder them to the slider switch.
Cut 3 appropriate lengths of heat shrink tubing and shrink over the wires that you just soldered to the slide switch.
Crimp one female connector to one yellow wire and one male connector to the other yellow wire. (With this done you can remove the WHOLE setup and passlock will be in original state).
Tap into the black wire (if using a 558 connector, connect the wire from pin 3 on the slider switch to this connector)
Connect pin 1 of the slide switch to the keyside (ignition switch) of the yellow wire
Connect pin 2 of the slide switch to the resistor you have soldered up or the variable resistor set to the right resistance.
Connect other side of resistor to the other (coming from BCM of car) yellow wire.
Set slide switch in desired postion and stuff behind dash
Replace the center air outlet
Images: Click to enlarge (a lot!)
Do note that I used telcom splices intially, but this wasn't all that reliable so I ditched most of them for quick disconnects