So I upgraded from an X910bt to the Z140bh this past weekend, the harness in my boxster doesn't have an illumination wire.

I've noticed that my z140 never goes to night mode, on my old nav it would dim based on an ambient light sensor so I never bothered to figure out how to get an illumination signal. Is my unit defective or does the z140 not have an ambient light sensor?

no such sensor exists on the Z. U need to hook up the ILL wire for it to work.