i know there's adaptor kits to accomplish this, but i'd like to think i'm pretty handy with wiring, there must be a straight-forward way to wire an audio source to the sat jack on the head unit? i don't have satnav (nor do i want it), but since there's still the input, i'd like to take advantage of it, preferably without dispensing much cash.

anywhere i could find the wiring diagrams of the head unit?

thanks,