After a year of course there is no reason to suspect anything other than what only the dead systems have in common. The radio will always have a 12 volt memory wire for the station presets and clock, and that will be tied in with some other circuit that is always live. The horn and interior lights are both circuits that are commonly used, so all three circuits have something in common; their 12 volt power feed. When you checked the fuses, did you check those under the hood? That is where you'll typically find those that feed multiple smaller fuses inside the car.
If there's no blown fuses under the hood and inside the car, measure the voltages on the fuses for the affected systems. If there's 0 volts on both sides, you have to work your way back until you find where you do have voltage.
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Sunday, November 4th, 2012 AT 5:45 AM