rear wiper working only when moist for 12 hours 2000 expy xlt

[Petesexpy]

My rear wiper is driving me nuts. The motor is about 2-3 years old and works fine when it works. It almost never works for me, works frequently for my wife. It only works if the car is damp after the night's rain - about 12 hours of soaking. I suspect ground or lift gate switch, but I do not know how to find either one. BTW, the lift gate warning light is fine - it lights up when it supposed to. Anybody have any ideas, or at least can help me with the location of these items? BTW, the motor mount is located on rubber busshings, so that's not where the ground is.

 

[Plati]

Would help to know the year of the Expy. You know about the well documented problem with those wipers getting "stuck", right?

 

[Petesexpy]

Would help to know the year of the Expy. You know about the well documented problem with those wipers getting "stuck", right?

Sorry, it's a 2000. Yes, I know about getting stuck. At first, tapping on the motor or around it would activate the wiper. Now it does not any more.