Andii

So my horn and my lighter won't work if the other is plugged in. So my horn wont work if the lighter is hooked up and the lighter wont work if the horn is hooked up. I bought the car like this.

Another issue is my power power mirror switch wont work either. Its driving me crazy!

TrimDrip

I'm pretty sure the horn and lighter have the same fuse. So, check your fuses first.

88 orangepeel notch

Sounds like you have a short in one of those, my guess would be the lighter socket. Mine was bad since the day one. I never use it so I didn't care, but checking with a multimeter will narrow it down. Same goes with the mirror switch, gotta find out where the power is going....