To be absolutely certain:
1. Consult your owner's manual: This is the best resource. It will have a diagram of both fuse boxes showing the location and amperage of each fuse, including the one for the sunroof (it might be listed as "power sunroof" or something similar).
2. Look closely at the underhood fuse block: It's usually a black plastic box near the battery. The cover should have a diagram printed on the inside.
If you can't find it after checking these two resources, a local auto parts store may have a wiring diagram for your specific year and model Impala. They're often happy to assist with this.
