Req Radio

I have a 09 Journey with Req Radio I would like to know how to hook up a monitor to the radio itself, know it can be done but. Can't seem to figure
out exactly what pins I need to tap in to. i hve found some good info but its also contradicking. I was told just hooking up the positive off an rca cable was all I needed. but I have tried this and doesn't seem to work. I believe the positive has to be hooked up also? if anyone has any info on this or has done this it would be great! thanks...
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