A bit after the fact, but I am going to install an after market GPS, DVD - do everything Double din unit as well as a dedicated rear vision monitor in a 2005 TI patrol. I would like to disable and remove the current nav unit and DVD as part of the process. Does anyone understand the complex relationship of these units. BTW I wondered what that was under the drivers seat..... And what are the complexities of getting the Steering wheel controls to work? Many thanks for any help.