Electrical issues

Thursday, I hopped in my car after hitting up Wal-Mart, and the radio display, car lighter, and internal lights weren't working. A blown fuse was determined to be the issue and was fixed after a quick stop at AutoZone. The next day, I stopped at a stop light, and the radio display, car lighter, and internal lights stopped working. The same fuse blew. Earlier, the same fuse blew again.

Any idea what could be the cause? I've narrowed it down to either the wiring has gone bad or that it could possibly be caused by the iTrip I recently purchased.

Also, my car is finally nearing the 100k mile mark. It's only taken it 20 years.