My Jap CR14 definitely has one, but my mechanic replaced it during a service so I can't tell you where its located, I'm sure your local dealer or mechanic will point you in the right direction (they can't charge you for a phone call, why not just give Nissan a call?)
Hi, mine has faded backlight problem; I have found a speedo repair company in my country that says they can fix it; so I guess it can be done (not sure about changing of the colour though ). try googling speedometer repair and see what you can find where you are.
To be honest my car was imported without a stereo fitted that's why I got a new head unit as my first job; my JVC has no real discernible gap around it and is quite stable, the wiring harness was supplied by the stereo supplier but I remember there being many types for many different vehicle...
My JVC head unit was fitted without any adaptor but a wiring adaptor was used to plug straight into the Nissan harness. Mine is a 2002 Jap import with the same storage compartment above the radio as yours.
Well we are back to a faulty head unit switch then aren't we? get a new one and be done with it or if you prefer your stereo to always be off you can just remove it completely and fit a blanking plate.