Hi Dan
1. You can use the earth at the lights.
2. I routed the cable from the boot through the passenger side rubber gaiter then down and along/underneath the passenger side sill trims then up underneath the glovebox to the radio.
3. The 4 wires don't connect to the interface. They have writing on them I think as follows
1. Wasser= earth
2. Steady plus = permanent live not ignition
3. Can hi = can hi
4. Can low= can low
All wires can be found at the back of radio rns510 has a sticker on top listing all the wires.
Earth and a permanent live are easy. If the are no can hi or can low wires at the back of the radio then they can be found in the drivers footwell just above the wheel arch under the dash. These wires are usually twisted together so they should be easy to spot.
Please note: if extending the CAN wires you must use proper CAN wire and do not use scotch locks
Hope this helps
Cheers man,
The girlfriend found the tiny labels on the wires of the kufatec. By the end on Monday I had it all working with the ignition on but as soon as I started the engine the RNS would display the multi-colour striped screen for a few seconds then it would just return to the radio