You really can't have done much searching on the forum have you?
There is a hole in the bulkhead in the middle of this picture. A rubber grommet, about 5 cm wide is easy to drill through. It can also be removed, but as there are elements as heavy carpet and sound proofing on the inner side, it is fairly easy to lever a small drill down there and fire through. Pull the cable through with a steel wire or similar. The hole must not be drilled too large. It must fit like a glove or even tighter to make it waterproof.