Not sure abt the e36 bro but i installed onto my e34 n no probs..
Just went to the local access shop n they cut a hole in the bumper n put the control unit in the boot..Cost abt RM 280..
It does engage when u shift into R but i dont think it works quite as well as n OEM unit la bro...but then again i think the price is just a fraction of it to!