Just finished hardwiring a Valentine V1 in my 2017 BMW 440i. Although I've learned a lot from previous posts nothing matched my configuration so I thought I'd repay the favor.
My car has the driver assistance package, lighting package, luxury package and technology package along with Apple CarPlay and wireless charging.
I decided to install the V1 above and to the right of the rearview mirror where it would be out of my field of view but still accessible. The passenger visor still works fine, though when it is down it blocks the V1's rear-looking sensor.
Even my thickest credit cards weren't up to the job so I opened the clamshell cover under the rearview mirror with a putty knife.
My car has two multi-connector plugs, a smaller red plug at the top and a larger black plug just underneath. I used a multimeter to find the ground, which turned out to be a brown wire with a black stripe in the small red plug at the top.
The multimeter found +12 volts on the green wire with a brown stripe in the large black plug, and the power on that wire went off when the ignition was off.
I bought a 15-inch Mirrortap from J28 and it arrived with multiple taps of various sizes. I think the 15-inch length would be fine whether you preferred to mount the V1 on the driver's side or the passenger's side of the rearview mirror.
The wires in the car's small red plug were smaller, maybe 18 gauge, and I found that the small black tap worked perfectly. The wires in the black plug were larger, maybe 16 gauge, and the longest red tap seemed to be the best fit.
Closeup of Mirrortap wiring:
https://goo.gl/KNOymm
My preferred placement:
https://goo.gl/dngnCI
An alternative on the passenger side:
https://goo.gl/zDbqI3