With the correct harness strickly plug and play - Unless you hook up the the VSS ( Vehicle speed sensor) but the Nav is pretty accurate without it. I would I would also ground the ebrake into the harness, that is what I did and no interference. I also tied the siruis into the harness so that it is all intergrated. Everything is easy if you do it this way.
Also the HK system sound about 100 times bettter just from the head unit upgrade alone. I changed NONE of the speakers. I wanted to prior to the install but now I doubt I will.