Fixing up the radio - I'm kinda confused
TLDR below with just my question
To start with, I am not very savvy with cars so forgive my ignorance. We bought this car just over two years ago from a seller on Facebook marketplace with only a little bit of knowledge going into it (not very smart, I know). We've had issues here and there. The guy that previously had it mentioned that he had a buddy who had worked on it a lot previously. It has been raised, larger rims have been installed, he said that the engine was replace/rebuilt (IDK how much I believe that but it looks clean)
Most of the work we've done on it has been aided by our neighbor who used to be a mechanic for 30+ years in Boston. We've replaced the clutch fan, raised the idle, replaced the thermostat, installed a new battery, and gotten the alternator rebuilt by the Mitsubishi garage. Like I said, it's been a plight to my wallet, but I love the little car.
Anyway, I wanted to plug in the radio. The previous owner said that they unplugged the radio because it killed the battery. He was using a lawn and garden battery, so I assumed that is why, however I am nearly certain now that this was a lie as I look at the wiring harness.
TLDR: Is there some sort of adapter I could get? Alternatively, what plug head is compatible with the radio? I want to keep the cassette player but at this point should I just replace the radio?