In my RHD you sit in the drivers side, remover the speaker grille/kick panel, remove the speaker and undo the two silverish screws below where the speaker was. Then stick your hand into the gap left by the speaker, prise up a kind of hinged plastic seat for the speaker, reach right down and you'll feel a plastic module. This is the CLCU, pull it out carefully because it's still attached to a kinda triangular bracket.
I guess for a LHD beamer you'd sit in the passengers side but otherwise it's the same!
Gone but not forgotten: '87 UK 318... Carb madness!
Currently: '90 UK 525i completely stock
"Heaven for the climate, Hell for the company."