There's two fuses; one for the switched 12 volts and one for the memory circuit. The memory circuit is typically tied in with something else that's always hot, like the interior lights, horn, or cigarette lighter. On a lot of newer cars the radio needs a turn-on signal from the Body Computer. Computers don't like reverse polarity from jumper cables hooked up backward, but it is very unlikely that computer could have gotten damaged and the radio is the only thing affected.

Answered by caradiodoc (expert)
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