This. That's what I did. Behind the steering column, up the a-pillar, along the headliner, and mounted behind the rearview mirror. No problems at all, full gps signal.
Can I do this if I take off the radio alone or will I need to take off both the dash and pillar?
I just did the center console and a-pillar. I ran it down under the steering wheel so I didn't need to remove anything there and used a coat hanger to route the gps wire up to the pillar. Then you'll need to pull off the weatherstripping and tuck it around the side airbag in a way that won't prevent it from opening. Then just go out through the headliner and you can conceal the wire along the edge of it.
Is the weatherstripping hard to remove? Also, what would be a way to place it so it wouldn't cancel the airbag?
The weatherstripping pops on and off very easily and basically you just run the wire around the airbag and not over it (common sense). Even if you were to run a wire over the airbag, it deploys with enough force that it would probably break the wire and wouldn't matter, but it's a dumb idea by any means.
