Once locating the fuse on the back of the head unit, pull the fuse out and check to see if the arch in the colored plastic is connected. If not, the fuse is “blown” and needs to be replaced. Replace fuse with the same amp rating and radio will power on.
How do you reset a Pioneer SPH?
Why does my radio have power but wont turn on?
Most probably, the power wires of the stereo are in bad condition. While one power wire is always out, the other only heats up with the ignition key. But, if their functions get inverted, the stereo will stop working. If these power wires do not have any voltage, it is time to replace them.