Radio / Converter

[Artist Formerly Known As CHINO]

Does anyone know if your stock radio can get damaged by
adding an after market Power Amp and Box through a converter?

I used the rear speaker wires(acting as RCA wires) to use the Power Amp through a converter and it seemed to work great for quite a while!

Now, a few months later, one of my lines from the radio doesn't work(right-rear speaker).

I tested all speakers and they all work.
I then proceeded to take the radio out and found out
that it's the line itself (negative/positive right-rear) of the radio and not the speaker wires.

Any Ideas on why could this happen; could the convert have anything to do with it?

I'm getting a new stock radio and do not want the same thing to happen again.

Any ideas ?.....