passenger side dash speaker cut out?????

One day in my parents voyager, the passenger side dash speaker just stopped working. I thought it was blown, so I replaced both dash speakers with pioneers. There is a pioneer cd player in the dash also. The speaker still does not work. I don't know anything about the wiring of a voyager, it's not my car. I have a 2000 blazer. I'm thinking that maybe the ground came loose, or maybe the harness needs to be replaced. I am pretty knowledgeable on installing car stereos and speakers, so tell me where to look and I'll find it. Thanks.

Go to http://installdr.com/QuickWiring.html for chryco wiring diagram . also pull out current head unit and check for poor splice or solder job , usually wires don't just stop working on their own , probably bad connection if the connector to the speaker is ok .