1991 geo metro radio fuse blows 15amp when I turn on the headlights

The illumination for the radio is tied into the headlight circuit. Remove the radio and check for a bare spot on one of the wires going to the radio. If this is an aftermarket stereo double check your wiring diagram connections for the radio. Pay close attention to the illumination wires. You might have a hot wire connected to ground by mistake. Hope that helps! Jim