The backup camera being rather unfocussed and slow, I decided to add back up parking sensors. Chose a cheap eBay 4 sensor kit with display and beep signal. Painted the sensors to match the car colour. Started by identifying the red coloured rear back up light wire (see picture below) in the cluster of wires running on the left wall of trunk. Used a feed from that to power the sensor box/brain with a red wire. A black wire from the box connects to earth/chassis. All connections are usually well shown in user manual accompanying the sensors. Drilled four sensor holes using accompanying drill on the rear bumper and rail roaded four long strings from the sensor holes to the inside of trunk through the rear left ventilation square hole with rubber flaps (see photos). The strings can be seen entering the sensor hole and emerging inside the trunk. To pull these strings through the hole, I used a long metal wire from inside the trunk and directed it towards the outer sensor holes, fiddly but doable. I then used these four strings to pull the sensor wire inside the trunk. Connected the four sensor wires to the box as shown in sensor manual. Push fitted the sensors in their respective holes in the bumper. Now comes the placement of the display. Stuck the display on the dash and tucked the wire behind the kick panel and drew the wire under the door sill all the way back to the trunk. The kick panel and door sill plate are dead easy to remove and re attach. Connected the display wire to the box/brain. Tidied up all wires and connections and tested and saw that it works. The photos are self explanatory.
Rear Parking sensor DIY in Auris E18.
Four rear parking sensor mounted without taking out the rear bumper and locating the backup light wire for power.