Wiring help

[PNW_S13]

I just put all new 6.5 inch speakers in my 1991 240sx and it was all fine and they all worked until i turned the volume past 20 then the sound cut and i cant hear sound anymore like everything is on and the speaker like pop when i turn the car on so i think they still work fine and the head unit still turns on and works fine just no sound. The first thing i did is get a new head unit and i installed it but but still no sound now i'm stuck and have no idea what to do please help. P.S I looked for factory amp because i believed that is was just blown but i couldn't find it so i'm very lost