easiest access to reverse light wire
 

I just got the Harman Kardon TrafficPro (really, a nice Becker CD Receiver/navigation system combo from Europe). Hookup hasn't been too difficult on my 87 Carrera, I tapped into the GPS/Speedometer for speed sensing, and the ash tray light for illumination cue, because these wires aren't provided in the regular stereo harness. The only wire I still need to hook up for GPS functionality is Reverse. I need to tap into either the reverse light, or the reverse light switch. Same circuit of course. Not sure where is the most accessible/easy to run a wire into the cabin from.

Can someone provide me with some hints? Like, does the wire run somewhere in the front trunk that I can tap into?

The reverse light wire runs from the transmission to the light assembly at the rear of the vehicle. If you were liying on your back under the car, you'll see the wire run into a connector on the left (passenger) side of the transmission.

Once tapping in, you could try running the wire into the cabin the same way I ran the RPM sensor into my DL-90 unit. On the drivers side near the bottom of the rear seat, there is large tube that runs through a hole from the interior of the car to the engine compartment. I used this same hole to run the wire into the cabin, under the carpeting, and up to the dash area. There may be a more elegant way to do this, but this sure was easy.