I?m about 99% sure that small silver plug is an AM antenna. If I remember correctly, there should be a thin line around the windshield that looks like a rear window demister. Either that or theres an extra strip on the rear window. We had those kind of radios come in on our import toyota surfs. We never had the time to figure out the wiring so we just re-wired the whole lot.

I think you?ll find that the speakers are kinda special with that particular combination. They?re mounted in little boxes with a passive subwoofer in there (a 4¿ diaphragm that vibrates when the speaker moves).