Alirighty, I thought i could be a big man and install this puppy for my friend here at work with no problems... of course, i was wrong.

This is in a '91 Ford Explorer with the "premium sound" package, meaning it has a factory amp and sub.
There was an aftermarket head unit in place before, which was stolen, thus prompting the empeg purchase. The thieves were nice enough to leave the factory harnesses in place.

I got the electrical part down pat, no problems. Bought a harness adapter, soldered on the Rio Car ISO adapter, plugged it in, boom, works.

Now the speakers is what i need help with.

The factory amp has a plug in the dash that is square, and has two sockets for each speaker, one + one -. So we went and purchased an adapter at a local install shop, and i went to Rat Shack and picked up some Male RCA plugs to solder on to it, so it could be attached to the empeg line level out RCA's. I thought i knew how to wire them up, but plugging it in proved otherwise. Here is a crude drawing of the setup:



Two problems:

1. Something is wrong with the fact that i wired the - wire to the shield on the RCA. When the plugs are completely inserted, the sound is garbled and muted... but when i pull the plug out so that only the center + pin is insterted and the shield isn't making contact, all is well. Should the - not be connected at all to the RCA plug?!

2. All the speakers work fine (as long as the only the + terminal is making a connection as stated above)... with the exception of the Right Rear. When it is plugged in, the sound comes out of the Right Front speaker, and is very muted. I've quadruple checked the connections and checked that plug with every line level plug coming from the Rio sled, so it's not a problem with the Rio. It's wired correctly on the adaptor, no crossed wires, no solder touching, no pins out of place. Does anyone have any idea what would cause this? All the speakers worked properly before with the Sony head unit, so as far as i know the amp is wired correctly from the factory.

Thanks for any and all help! He's dying to get it working, as the hour long commute from South San Francisco to San Rafael is murder without tunes!