@GreenGL writes:
The official Volvo instructions say to drill a hole near the fuse box, but I would like to avoid drilling holes in the car if possible.
Having not seen the official instructions, where does they recommend mounting the sensor? And, are the instructions designed for LHD or RHD in mind?
Have a look / see for spare grommeted holes in the black 'hatch plates' which are bolted to the firewall. Depends if your car had aircon (if not, 2 spare holes) automatic (if so, spare hole for clutch) pre-86 (if later, spare hole for speedo cable on the RH plate), etc.