Thats a bit odd. Perhaps it had an after-market setup and the
stock radio was put back. I'd disconnect the red wire and then
pull the radio out to inspect the wiring behind it. To do
that push in on the two tabs at the botom corners of the
radio (use a coin). They will pop out (they are mini handles).
Pull on the two handles to pull out the radio. Then you can
visually inspect the wiring behind it for any obvious electrical
shorts. Stock, there are just plug connectors that plug into
the back of the radio. They are typically wrapped with some
foam to prevent rattles. So, you should not see any cut and
re-connected wires, electical tape, crimps, wire nuts, etc.