There isnt really a simply diagram to follow as such however when i get home i will take a photo of the connections i have had to do and how i striped the phono cable because if u strip it incorrectly u will here a permanent buzzing or interferance sound coming from the sub which is very annoying, and ill tell u which part of the cable goes to which wire on the steering wheel control plug after that it should work a treat, have u got the option to adjust the subwoofer setting in the sony headunit u have??

Regards Danny