No radio reception with Rockford 9110G and antenna adapter

[hccyong]

I was testing out my new Rockford Fosgate RFX-9110G today in my 1995 318is. Unfortunately the radio functions as if there is no antenna even though the antenna is plugged in, through the VW10 antenna adapter from Autotoys. I didn't get a chance to test the continuity of the adapter itself as my multimeter was dead. Is there something else that I should look for? The stock radio (without using adapter) works fine. As far as I know, my antenna is in the rear window, and the signal is amplified by an amplifier in the left C pillar, so I do not need an amplified adapter (which I confirmed with others too). I can't figure out what is wrong. The adapter is a very snug fit into the head unit's socket, but I'm sure I plugged it all the way in. The antenna harness that comes out of the dash does have another lead that I'm not using, but I'm pretty sure that's an additional chassis ground or something since the stock radio works fine even without this extra wire plugged in. Thanks for the help.