e46 double-din install problem (wiring)

[zhuzhichao]

I am reading through the posts of others' installation write up. I am gonna install kenwood dnx9140 but still have some questions before I can start.

I am looking at this wiring diagram:
http://i86.photobucket.com/albums/k8...ingdiagram.jpg
It says I cannot directly connect the ground wire from the head unit to the ground wire from wiring harness, but should connect the head unit's ground to vehicle chassis. So what should I do with the black wire coming from the replacement wiring harness? Should I also ground it to vehicle chassis? I am using Scosche Vwa-3B wiring harness if it helps.

Now I have three ground wires (head unit, backup camera and pac swi-jack) that need to be chassis grounded directly (I suppose I can tap them together then ground them, please correct me if I am wrong). And I have three red ignition wires from the same three units, can I just tap them together and connect to the red wire coming from the wiring harness? I am not sure if it is OK that I can just tap them like this or I need to connect the other two red wires (other than the one from head unit) to the fuse box. Would them get enough power? Please forgive me I am not good at elec flows

My car has HK system. Does the wiring diagram you provided also works for my car? I mean the factory amp and all the speakers will work fine?

Thank you so much in advance that you take your time to answer my questions.

[Technic]

This is the forum that you need to ask that question: www.e46fanatics.com