Has anyone installed an aftermarket stereo with built in GPS?

I just picked up a Pioneer AVIC-F700BT (double din) it has it's own GPS antenna but I don't want to route it to the outside. I'd like to keep it simple and put it on the dash. Will I see any accuracy or interference issues?

 

Also, in order for the GPS to navigate properly I have to tap into the reverse lamp wire (aaaaaallll the way in the back). If I could find where this wire is under the dash that would save a lot of headache.

We have had pretty good luck installing the antennas WAAAAY up under the dash. As high as you can get it. Just keep it away from any high-current items like the blower motor and you should be just fine. For best results, you should run the antenna to the outside. The antenna will work better with a good ground plane and a clear view of the sky. It will work under the dash, but not quite as well.