everything is not isolated, they are just ran in parallel not sequential circuits. so one burnt bulb won't kill the circuit (like with cheap Christmas lights, which are sequential)
each fuse can have several systems running off it, or just one, depending on the amp-load. several small things, like stereo, dash lights, instrument cluster, etc, can and usually are ran off of one fuse.
it's very likely that the radio, dash lights and instrument cluster share the same fuse. they are in the same area, and often share a fuse.
so just tape those wires so they don't ground again, and then look through the fuses with a penlight and find the burnt one.
