Re: Old car radio - how to change polarity?
Either you can change the radio with a built in switch, or you can't.
It's maybe 20 years (more like 40) since cars had dynamos and could be changed to -Ve from +ve or vice versa. I think I may have done this in the mid 1970s (+ve to -ve for a new car radio).
It the radio has no internal switch, you need a DC to DC converter as the aerial and case is very awkward to insulate and you risk shorting the supply.
It would be really bad idea nowadays to swap a car to +ve earth, even if you could. I'd only swap a vintage or classic car to +ve, that was originally +ve and converted to -ve, as part of a restoration.
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