Why won't my head unit turn on?

I have a 1995 Honda Civic Hathcback. I just replaced my alternator and after i did that, my head unit will no longer turn on. The head unit itself still works, just not in my car, and none of my fuses are blown. My cigarette outlet still works and its on the same fuse as my head unit, which doesn't work. I didn't know if this was a common problem people have, but I can't figure out what's wrong with it.

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