40a ign fuse blowing?

Hello, after you removed the starter and did your checks and found the circuit through the starter relay is shorted to ground did you put the starter back in, or did you try energizing the circuit with the starter disconnected fully?
I've got both aftermarket and OEM diagrams below. I just wonder if the starter motor is in the mix here when that fuse goes. 40amp is a pretty high amperage, there's nothing else in that circuit after the fuse except going through the relay to the starter motor, but that is after the starter solenoid has been closed. If that fuse is only blowing after the starter is hooked up it has to be something in the starter itself. Are you hearing the Starter solenoid click before the fuse goes? Or is that missing as well.

Check my last post, I'm wondering if it's something in the starter itself. I posted diagrams as well.

Try this: hook up the main 12v to the starter post but leave the smaller starter signal wire off and see if it's a short in the starter. So, leave the solenoid wire off.

Okay, interesting case study though, it can't be anything on the ignition switch side because that is isolated by the relay. I don't ever fully trust wiring diagrams either. They tend to be incorrect more than people think.
This is what I was afraid of, these diagrams are all different, some show the ign A 40amp only feeding the starter relay, but others show it running through the ignition switch and going all over the place.
If these other diagrams are correct and that fuse feeds other circuits I've narrowed them down.
On the bottom left of diagram 4 there are other component names highlighted in yellow and they are in the 5th diagram. If that main fuse is still blowing with the starter unhooked, then we can pull the fuses for these other components to figure out which circuit has a short to ground.