Im new to the industry so sorry if its a dumb question but i must ask, how do you test the rain sensor before removing the old glass to ensure its working properly. No one at my shop knows and had a 1659 to do today and the customers rain sensor wasnt working after we installed the new glass even though we replaced the pad. Is there a certain setting the wiper switch needs to be on or should they just automatically come on if the water hits it? Didnt see anything in the owners manual.

How about asking the vehicle owner to show you how it works and have them show you it does work. A novel idea.
Ooops.....

turn key to run position followed by turning on wiper switch on low setting. Spray windshield with glass cleaner multiple times. As the wipers clear the windshield spray again right away and the wipers should clear automatically.