A part of troubleshooting your car stereo system when it won't power on includes checking the fuses to see if they need to be replaced. Fuses are used to protect electronic devices, such as car stereos, from power surges that can otherwise cause extensive damage to these devices. Car stereo fuses are easy to diagnose, and they're also very easy to replace. They come in several shapes and sizes and often there are multiple fuses in a car stereo system, but no matter the size, shape, or location in the automobile, it's easy to find out whether the fuse is blown or is still in good shape.
Disconnect your car battery for safety purposes, and then find your car's interior fuse box. It is often located near the feet on the driver side or near the glove compartment on the passenger's side. If you can't find the fuse box, consult your car's manual to find out where it is located.
Pop open the fuse box, and find the fuse labelled "radio" or something similar to that. Your fuse box should have a diagram labelling each fuse on the outside or inside of the cover. You may have to inspect several fuses to make sure you're checking the stereo fuse. The fuse will most likely be a 10- or 20-amp fuse, and you can tell by the number label on the fuse itself.
Use the needle-nose pliers to carefully pull the stereo fuse out of the fuse box.
Inspect the fuse closely in the light. If the metal material inside the fuse is separated or you see a blackish film inside the fuse, the fuse is blown. If the inside of the fuse is intact and doesn't look damaged, put the fuse back into the location it came from. Make sure it's pushed all the way in.
Replace any damaged fuse with a fuse of the same amperage. Fuses are colour-coated, so the replacement will most likely be the same colour.
If the car stereo still doesn't power on after you've replaced the damaged fuse, you may have to pull out your head unit (CD player/radio) and inspect the fuse on the rear of the head unit using the same technique as above.
Keep a supply of car fuses on hand; they do need to be replaced from time to time.
Disconnect your car's battery when doing any type of electrical work. Make sure replacement fuses are the same amperage---don't use higher- or lower-amp fuses.