E46 318ci convertible PDC unit

[BD]

Hi All, I have brought a 318ci convertible 53 plate a few months back and the reverse sensors don't work there is no clicking so I have brought a PDC unit but I cant find where it is I have looked behind the boot trim on the drivers side but nothing that I can see. Can anyone help!!!!

I hope I have done this right but I haven't posted anything before.