Ground loop? Or wiring mistake?

I have a '97 Suburban and it has the seperate radio and cd player.  I pulled all my audio equipment out of my '94 GMC Sierra and was installing it in the new vehicle (suburban) and realized I needed a line converter.  I ran over to Circuit City, and even though I didn't want to have to use the factory radio, I'm too lazy to replace it with my aftermarket from the old truck, so I got the converter.

Here's the problem.  While taking out my factory speakers in the front doors, I checked the polarity and wire colors coming from the speaker and the front right is fine.  When I hooked the wires up to the converter from behind the head unit, and ran the RCA's to the amp and it was all said and done, it's great.  But the front RIGHT channel won't play.  If I fade it to the front right, and crank on the volume I can just barely hear music.  I've checked the other channels by fading and balancing and all the rest are working, so I MUST have the correct wires, or at least that's what I think.  The front right cannel for the suburban is a dark green and a light green.  I don't remember the polarity at the moment though.  So my question is this.  Is it possible that I have it backwards with the polarity and that's why it won't play?  OOORRRRRR.... (suspensful music playing) here's the other thing.  There's a brown wire coming out of the converter.  I was told that it's just  a ground loop, and unless there's a harendous noise coming from the speakers then don't worry about it.  Well, I connected it anyway and nothing new happened.

So does anyone know the "correct" wiring for a '97 GMC suburban?  I.e. which wires are for the front right speaker and the colors and polarity?  If I get nothing by this afternoon, I might just run over to an O'Reily's and get the car owner's bible.  LOL.  (Haynes manual).

Your line converter sounds like the kind I sell, and they have a "gain" control built into them, if so, try playing with that and see if that fixes anything.  Front right color code is light color +  dark color -.