Where is the fuse for the radio on a 2000 Nissan Sentra?

Answer 1

Under the hood, right next to the battery, there is a fusebox. There is a 15A fuse in this fuse box labeled audio.

This is the fuse that interrupts the default power signal for the stock radio.

Most aftermarket radios rely on an adapter harness that changes the stock wiring to the standard wiring making it easier to connect the replacement radio, so I would say that in about 95% of instances this is the fuse that you would check first. It is my experience that even if your aftermarket radio has a fuse directly on the rear of the headunit, you most likely blow the primary fuse first.