A couple of questions:
Are you in an urban area, and
Presuming you were doing the setup in your driveway, or somewhere similar, have you tried going to another location and running the setup?

 

Pull the radio out and make sure the Sirius antenna is plugged in. The previous owner may have removed or replaced the radio and never plugged the antenna back in if he did use the service. It's only 5 minutes work to pull and check.

 

I live in a small town, and I did try the setup in the driveway. My understanding is that even without the service, it should connect to the Sirius preview channel, and it won't connect to that anywhere, even out in the middle of nowhere. I did try pulling the radio and disconnecting/reconnecting the antenna, but no difference. Does anyone know how to get the antenna off the back so I can make sure it is connected properly there? Otherwise, I may be looking for a new/used radio. I guess that's not too terrible. Everything else on the van works great.

 

When you pulled the radio, were there 2 antennas? One for AM-FM and one for Sirius. The AM-FM cable is slightly larger in diameter and plugs into the white connector. The Sirius plugs into the yellow connector. I'm not sure if it's possible to reverse the connectors. Is there an antenna mounted on the roof at the rear just ahead of the spoiler? It's about 2" x 3" x 3/4" tall.

 

Buster, yes there are two antennas connected and the antenna does exist for Sirius on the roof.

 

That only leaves 2 possibilities, a bad antenna or lead, or the radio itself. What radio do you have? There is a 3 letter code at the bottom right hand corner of the radio. RES, RHR, RHB, RBZ or such.

 

It's an RBZ. How would I test if it's the radio or antenna?

 

Well, I took a chance and found a replacement radio through Ebay. It fixed the problem and I now have Sirius radio.