Radio and Speakers questions

Hey guys
I've recently tried to bring my radio back to life. It has never worked since I've bought my car back in 2022. The in line fuse together with the holder on the main wire was melted, so I got a new set of fuses, aswell as the wire block connectors for the radio - speaker connection. The radio now seems to be on, at least there is a light when I turn it on, but there's no sound.
I've taken out the speaker to test it with the battery test. There is some rustle, but pretty silent. I've tested it with a normal 4.5V battery.

What is an easy way to test if the radio is the main problem? I have no idea how to use a multimeter, to be honest. As many people already said: Electrical stuff is like Voodoo to me, aswell. Can I just hook up a random stereo speaker?

The speaker when I've pulled it yesterday.
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I couln't find out the model of the radio. There's a sticker on the lower side but I can't read it because of the heater. I'd have to pull out the radio but the metal knobs seem to be stuck. I have another radio which I was able to pull very easily but the one in the car is just stuck. Are there any tips?
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Just something for your eyes:
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