The Chevy was blessed with a fiberglass top, so you could just throw the antenna in the storage area over the front seats and get great reception. Sprinters have metal roofs so that's not an option, and radio installers usually place the antenna under the top cover of the dash, as far forward as possible, and try to get a signal through the windshield.
I have a heated windshield, with tiny wires embedded in the glass about 3-4 millimeters apart. You can't really see them, but these little wires make it hard to get an RF signal through. And I have a windshield cover I put in when we park – it's foil and bubble wrap stuff. And when it goes up, the signal disappears.
What I needed to do was get the XM antenna out where it could get a decent signal, which in a metal box means outside on the roof. I had it outside on my Crown Vic and never had a problem. The antenna is a little lump about an inch square with a magnet to mount it to your roof, so it's just a matter of getting a wire through the body shell. My idea was to run the wire through the penetration the over-the-air radio antenna mounted in, top center above the windshield.
Time to dig into the dashboard. Out come my trusty set of panel poppers, which are miniature pry levers and crowbar looking things installers use to take these plastic panels off without damaging them. The Roadtreks have a wood-grain applique over the panels, and I'll have to listen to years of recrimination from Sharon if I scratch them up. To her, they're the most impressive upgrade Roadtrek did when we built the van.
Sylvana put them on. She asked me the next day how Sharon liked the photos of the completed job, and I told her Sharon said they were so beautiful and then started crying, which for some reason means she liked them. I do not understand women. Sylvana does – she was very flattered. And they ARE beautiful. If you lived in a parking lot for five months at the factory, maybe you'd cry too.
The center surround pops right off, and you start seeing screws- lots of Torx head screws. Luckily for me, the Germans ensured in their tidy way that the screws are all identical, so you can just throw them in a pile as you take things off instead of having to keep track of where they came from. The air conditioner controls, the side panels with the air vents in them, and the map pocket thing above the radio all come off, and the radio comes out with four screws.
The XM antenna is all the way forward under that grill between the map pocket and the windshield. Lo and behold, I had two of them, probably the one on the left being the GPS antenna, or maybe a radio antenna that Mercedes puts in as they assemble the dash so it doesn't have to come back apart to hook up a satellite radio, and the one on the right was from my (aftermarket) radio we installed when we built this unit back in 2014. Which one is the functional antenna? I can't follow wires back to the radio because of the jumble of harness, so I solve the problem empirically – I stick one of them out the window and see if the signal improves. It does. Mystery solved.
Now I have to get this inch-square antenna from where it is to where I need it. I pull the panel over the right side of the dash, run the wire underneath it, up the passenger side A pillar (that's the metal support between the windshield and the front passenger side window) to the headliner, across to the center, and now I am ready to feed it up through the hole to some fresh air and strong radio signals on the roof. I have a 2013, so it's easy – pop the overhead light unit out and there's the nut holding the regular radio antenna on. 2014 and later models have the functional equivalent of a NORAD outpost up there with all the lane assist and blind spot monitoring, so yours may be different.
I have to saw the hole to enlarge it enough to get the antenna through, prompting protests from the back of the van. Be careful with the antenna, they are glued on and very fragile. I used a foot-long pry bar and eased it loose, pulled the XM antenna through, and then re-glued and reattached the over-the-air antenna. The XM antenna is black, so it is very inconspicuous on the roof – I ran the wire straight up to the central black three-window decal, and you can't even tell it's there. See? I told you those decals were good for something 😉
I test the reception for satellite and over-the-air radio, both work great. Now comes the reassembly. Back in goes the radio, the air conditioning controls, the side panels, the map pocket, etc., etc. It's a three dimensional jigsaw puzzle, but an easy one because of all the good engineering. Don't try to force anything – there's a way it goes together. the two grayish side panels with the air vents in them have hooks on the top – they go in and slide forward to lock into place.
It took me about two hours for everything, and now I'm very happy. Satellite radio is important for us for the same reason we have satellite TV and satellite internet – where we camp, there isn't much coming in via cellphone network or over-the-air broadcasting. All our connectivity is up there in geosynchronous orbit.