Ok, so I spent a whole day playing with this to get the best signal possible. But basically what I found to give the best signal was to have the + of the rca cable go onto the FM antenna on the board, and the - of the cable to go onto the AM connection on the board (farthest from the FM). I also tried using the - of the RCA cable to go onto a ground location on the car but that made it so much worse.
So my setup is basically this: rca (+) wire to FM antenna, rca (- or shielding) wire to AM antenna connection. Out side of the Radioshark all you see is a Female RCA port. On the car end, I have my stock antenna that goes into a Motorola/BNC adapter, then I have a BNC to RCA male adapter. So ultimately in the car I have a Male RCA, and on the Radioshark I have a Female RCA. One thing that I did notice was the signal got a lot better if I pushed all the adapters together, because the stock antenna isn't forming a good connection witht he Motorola/BNC adapter. So what I'm going to do is get this:
http://www.crutchfield.com/S-LAr89Yi...display=XL#Tab
I will cut this in the middle and solder the wire ends to the Radioshark. This way I'll have a female Motorola plug on the Radioshark, which SHOULD plug in with a good connection to my car antenna plug.