And here I am!
I indeed had the exact same tv/satnav installed in my GT4. It never worked either tho. The previous owner of the car also couldnt get it to work.
I eventially took it out and sold it to a fellow member on here last year. I had noticed tho, in my boot there are a set of clips that look like they would of held an ariel in place and clips running up the inside of the boot to the celing carpet. Possibly an ariel for the tv unit. But there is no wires or ariel there now. Looks like it had been romoved before hand.
My mate had a GT4 a few years ago and suprisingly, it had the same unit too, and his was a no go as well, so, sorry I can't really be of any help unfortunatly.
Hope you can get yours working as it would be quite cool to see it in all its Jap goodness!
My old satnav tv unit