I've read a couple of threads where people just mounted on dash.

I had mine on roof of old car, but tried dash on my new TL. I have it in left corner right about where VIN number is. My signal is not as good and it fades in and out quite a bit. Maybe if I went more towards the center of the windshield?

Curious where others have mounted and pics if coming in from outside to show where wire was run.

 

I mounted mine center of the back dash, and I always have good reception.

 

I connected mine to the OEM XM antenna via an antenna. I ran the wires all the way from the XM tuner in the trunk, up the passenger side, around the front passenger foot-well, and into my receiver. The installation is as clean as can be and I can't tell the difference as compared to the Sirius antenna when it was mounted in the front middle of the front dash.

 

I mounted mine on the lower left corner of the windshield and unless you look at that spot you can't even see it. Ran the wire under the driver's seat to the center console since that's where I have my radio connected to the AUX port. It made sense for me to do it this way since my '07 TLS has the AUX port. I considered connecting the radio to the XM antenna (there is a guy on a different forum that sells the cable) but it did not make sense price-wise. Reception is great and I did not risk paint damage by mounting it on the roof.

 

my reception is not good on top left of dash 1-2 bars and fades in and out. How far left or center did you go?

Also, is there a good thread that shows (with pics) how to remove panels to get to back of stereo?