Headlight switch backlight dimmer blows horn fuse...???

Lord I get tired of asking this. Year make and model. And yes, it is important. And no I cannot guess from your avatar. Dash lights get their power from the tail /park circuit, which feeds the dimmer control, and the dimmer control feeds the inst fuse in the panel, and from there onto the dash lamps

"Twist" of the light switch also grounds the low end of the courtesy lamps