range rover vouge mk3 head unit upgrade

hi all posted on here a few weeks back on reguards to my fibre optic audio system dieing mid way though in my eyes one of the best albums ever made haha. well trying to diagnose this devils child didnt go well so came across a full head unit upgarde were i can get rid of all the bits in the boot apart from the amp and sub and all be rock n roll providing the amp and sub are ok. so all the bits came today and im finding it very hard to find a wire diagram for the grey block that gose into the back of my stock screen as i need to chop into it to get a ground, key 1 and key2 live from help please guys i believe in you all haha.

thanks in advance Frank

Dont like to point you somewhere else but you might like to wander over to the fullfatrr forum one or two on there have had a go at this sort of thing.