1994 E320 Sunroof
 

I know I ask about this once before, but I received no help. My sunroof will pop up by using the sunroof switch. It will close from popped up position via the switch. It will close if I go to the trunk and turn the emergency shaft. The sunroof will not slide open or closed via the switch.

My question is: How do I test the switch? Rather than blow $50 on a switch, I want to isolate my issue to the switch specifically. Any help with this will be much appreciated.