No. If you are using the InterLink it will have a second connection cable to go to the 788ci unit. The 788ci will be able to use its own internal GPS Receiver. In fact if you use an InterLink I would go into the menus of each unit and set them to always use their own local internal (788ci) or local external (998) GPS Receiver.

If you are not using the InterLink than there are no connections between the 998 and the 788ci units.