What's the issue when headlights don't work on 2005 Chevrolet Trailblazer

My nephew put a new radio in, when he was finished, I had no headlights, the ac didn't blow out air and some other lights did not work as in the radio and inside lights.

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1 answer
The simple answer, and probably the issue, is CHECK YOUR FUSES. Then, if they are all good, you need to look at a wiring diagram and see what he "might" have tapped into.