I have not seen the Navigation unit in the Glove Box, but I was told that is where it goes if you get the Mazda Unit. But looking at the picture in the Mazda 3 manual it mounts above it.

You should have about 3 inches between the back of the gove box to the firewall. The end of the glove compartment is about 3.5 inches tall also. I will get some pictures up later.

 

no at no point do you need to touch the head unit. you do it through the actual rear speakers, meaning you have to take off the door panel to do it. at no point would i touch the head unit wires. that could do something huge. it could screw up your whole system. you must do it through the wires in the rear door panels ill take pictures and show you exactly what i did