Jim, the boot amp comment was for Steve McF!!
If you need the aerial amp...
Right hand (the one you have I think, 12792122 about £250
Left hand (if you already have both sides connected) 12792123 not sure this is current price about £125
The "kit" for adding the second aerial amp on the left: 32025554. About £250
The shark only does the GPS and the old carphone kit aerial - only needed before modern bluetooth handsets.
I can't help with the aerial amplifier earth. I think there's a possible error in the Saab manual.
Both the saloon and the estate have the aerial amplifier. The saloon puts it behind the trim on the rear pillar. The manual says it sits under the rear side window.
The saloon diagram shows a power feed, earth and the aerial return to the head unit. The earth is shared with the heated rear screen.
The estate diagram shows the same power feed. It shows the aerial connection back to the head unit, but no earth. So i don't know where the earthing point is. It's possible that the aerial amp is earthed via its mounting bolts. But the earth on the estate for the heated rear window is a bolt that is on the body of the car, not far from the aerial amp... The manual does not list the amp as being connected to it though. But who knows!!