Sat Nav Upgrade

[dransfield]

Hi

I have a 2004 Avensis T4 estate, the original 'turn by turn' sat nav above the central air vents is faulty and I was wondering if anyone had successfully installed the later sat nav with screen that fits in the same position, it looks like a modular unit that would fit in the space ok and it has a different box that goes under the passenger seat, but does anyone know if the wiring harness behind it all is completely different so would be a waste of time trying? 

If not I'll upgrade the stereo instead for a gps setup as there are plenty available but having a non working bit of kit in the car would bug me!

[G6-R]

normaly when you buy a orignal later model radio / satnav the cables wil fit directly