I believe my reversing sensors were 'main dealer' fitted after buying my truck new but there is no need for the dash switch, different specs etc, just ensure the wiring is hooked into the reversing light circuit and there won't be any problems.

 

checked everything, and parking sensor is indeed installed. All the sensors are properly plugged and the speaker does work, albeit its sound is very shaky so I guess I'll have to replace it. I may found it annoying at some point; but super easy to remove by unplugging the white socket in the picture.

Thanks for your help everyone!