All your lights are controlled with the light control module. This is essentially a computer that turns the lights on and off depending on the switch's inputs.
To test the switch...
Make sure that the switch has a good ground. (black/white wire). The switch supples a ground to the Lighting control module when the switch turned on (Gray/black wire) the lighting control module then turns on the parking lamps (brown wire out of the module).
To test the module...
At the lighting control module check the orange/black wire for 12v. Also check the orange wire for 12V. If the switch grounds are there and the powers are good, the lighting control module is bad.
Here are a couple of wiring diagrams to help you out. If you have any questions, PLEASE ask. Some of these parts are expensive, so ask if you are unsure of something.
Your lamp control module is located LH side of the dash under the instrument panel. Sorry for the long response. Let me know if there is anything else.