Sorry I'm a little late to this thread but I will share how I connected my radar detector and maybe that will help. It has been functioning perfectly since October.
Here's what it looks like now:
The cover behind the mirror was a bit tricky to get off at first since I wasn't sure how it was attached but it just has 4 clips that need to be pushed in one at a time and then the main body pulls straight off.
The location I decided to use is the connector to the mirror that powers the auto-dimming. This was mostly because of location, ease of access, and the blades on the tap fit without too much effort. Red/Yellow for fused ignition power (no power when car is off), Black for ground, and Purple for control (light sensor, do not use).
After that it's just a matter of routing the wire and putting it back together.
Hope that helps! I also have a dash cam but I routed an extra long wire though the headliner and down the A pillar to the fuse box under the dash and tapped into power there because, as far as I know, that's the closest location to find direct power from battery even when the vehicle is off. I want my dash cam to still work in 'park mode' and it won't without power all the time. I can post some photos of that too if anyone is interested.