1991 ford f150 gauge lights dim?

[brad88892001]

I have a 1991 ford f150 and when previous owner tried putting in a cd player he didnt tape the hot wires right and he said it killed his cd player but now at night when you turn on the lights at night the gauge lights inside are so dimm you can see them....they aint out just very dimm...does anyone know what causes this and how to fix it....

Thanks