Fuses are used to protect electronic gear. Aftermarket car stereos, like those made by Pioneer, come equipped with a fuse, either plugged into a slot on the back panel of the stereo (normal for Pioneer models) or attached in-line to the car stereo's wiring harness. If your car stereo has quit working and you cannot determine any reason for it, there's a good chance that the fuse may have blown.
Remove your Pioneer radio from the dashboard or other location where you've installed it. The exact dismounting method is beyond the scope of this article--there are literally thousands of different cars in which a Pioneer stereo can be installed. Take the radio out by reversing your installation steps or consult a car stereo technician.
Turn the radio so you can see the back panel. Disconnect the main wiring plug on the back of the radio by unplugging it. You'll see the fuse, located below the plug's jack.
Grasp the fuse with a set of tweezers or a fuse puller and pull it straight out. You may need to wiggle it slightly to loosen it initially.
Place a new 10-amp fuse into the slot and push it in firmly until it won't go in any further. Plug your radio back in to test it. If it still doesn't work, call the manufacturer.