I bought my Mazda with no radio I buy everything for a aftermarket one and it don't work, all fuses are good my wires are connected goodie have no idea what it could be plus my interior light don't work either would they be connected together some how?

 

There is one wire going to the radio that has 12 volts with the lights on. On some cars it is a black wire. If you used it as a ground your interior lights won't work and it will destroy the light rheostat, and if you used it as a ground the radio won't work.

 

All I did was match the wires for the radio the lights were never working

 

poor boy,
I've installed one aftermarket stereo
everything goes well after correctly installed