2004 vw beetle antenna issue?

Ok, here's the poop, I took out the deck (thanks to a vw keyset loaner from a good friend) and I had a look (took out part of the headliner) at the antenna, and the connector, etc.

The rear of the deck where the antenna attaches looks great, brand new in fact, solid connection, no burn marks, everything is great there.

I have a full spare antenna set (the part that holds the antenna, and the antenna itself, this also has the wire running from the antenna housing), and I connected that to the wire in the headliner, no noticeable difference.

I have a few more questions. 

1. How is the antenna grounded? Through the deck? If so, where is the deck grounded to? Through the wire harness?  Could this be a grounding issue?  Although the wire harness looked good, it's tight, maybe one of the wires is loose?

2. The 12V you guys talk about, if it's through the centre pin, how would you suggest I test to make sure it's good? I have a DMM.  Also, is there a way to test to make sure the ground is good? The ground and the power coming from the deck and near the antenna itself?

3. I just want to narrow down the issue, because if I go and get an aftermarket antenna and find that that doesn't fix the problem, I don't want to have wasted all that money.