I'm replacing my stock 3rd gen HU with the aftermarket one, thus I had to get the antenna adapter. So I went and got it from Wal-Mart. While installing it I noticed that in the adapter only one terminal is wired. The second terminal jsut isn't there - there is just a hole for it.
Long story short I've tried 3 different stores and checked adapters of different brands - in all of them there is only one terminal connected. For the second one there is either just a hole or it's not connected.

So my question is have you guys noticed such a thing when you were installing your HUs?
I realize that this means that one antenna is not working anymore and this could've been fine but I got a really crappy FM reception with the new HU, whereas radio reception on stock HU was just great.