Installed after market stereo, satnav no longer works

[Morgz84]

Ok, I think I know the answer to this but would like confirmation please.   I installed an aftermarket Sony headunit with the relevant wiring and facia adaptors, but Sat nav no longer works.   Would I be right in understanding that the Satnav is built into the factory stereo system and the lump on top is just a screen?   I don't use or need satnav very often so I might replace the nav screen with a mount for my tablet if this is the case.