Windstar Bad Ground?

I posted a message about my rear wiper not working in my 98 Windstar and saw some others with the same problem. Most of the suggestions
were to check the rear ground. I dont have a voltage meter and would have no idea how to use one if I did. Can I just the replace the ground wire to be safe? How would I go about finding where its connected to. Any help would be greatly apprecieated. Thanks John
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