Site for placing an electrode in auditory brain stem Implant is:
Ref. Diseases of Ear, Nose and Throat. Pg 127
 
Auditory brainstem implants have three main parts:

A microphone and sound processor positioned behind the ear to pick up sounds
A decoding chip placed under the skin to transmit information picked up by the microphone
Electrodes connected directly to the brainstem(4th ventricle recess), when stimulated, alert you to sound
Sinus tympani
Recess of fourth ventricle
Round window
Lateral ventricle