Just to be sure, you did say that it still blows with the head light sw. unplugged? Correct. MATT
That fuse (F10) , is the power source for the Igniton switch. Then the Ignition sw. sends power on to other components. For example the radio and the inst. cluster. You could start by unplugging the radio, It could be the problem. This will at least rule it out. I'll post some diagrams that will help you.
The problem could be the ignition sw. itself. It's tuff when it doesn't blow everytime. You'll need to test for the short during that window when the car is hot.
One method I like to use when looking for a short is to use a sealed beam head light. Like from an older pick up truck, etc. Connect jumper wires to the light, and then in place of the fuse that blows, connect the wires. So use some crimp on terminals from radio shack, etc. that plug in like the fuse would. In other words, you have the light connected in place of the fuse. Power will flow thru the light, until the short to ground happens. When this happens the light will light up, instead of blowing the fuse. This saves fuses, and you can place the light where you can see it. Start unplugging things that are on that circuit, or wiggling wires. When you find the problem (when you remove the short) the light will go out.
So if you unplug the radio and the light goes out, you know the radio is the problem. If you wiggle the wires at the column to the ignition sw. and the light goes out, then you need to look closer and find the shorted wiring. Hope this makes sense.
here's the diagrams showing what's on that circuit. Let me know if you need anything else, happy to help. MATT