top, both sides.
first Open base. take bottom off.
use low speed as the plastic is low melting temp. I use 1mm drill bit on a dremel tool. use depth stop if u have one. or mark with tape on drill bit.
I put a few holes extra holes bottom.
on both sides, there are ribbon cables. I use a thin metal strip between housing and cable to stop the drill bit damaging any cable.
you can disassemble whole unit. but I did not.
I drilled close to middl align to the processing board and sensor chip. ten holes on each side in two row s.
ten holes on top.
clean out plastic burrs inside housing so not cut into cable.