It makes no sense that the main fuse should be blown yet the 10A IGNI is still intact. Is there a bigger fuse in the 10A IGNI slot?

 

I agree, and no. there are three mini blade-type 10A fuses in the holder: IGNI, another that I forget what it was marked, and SPARE. The main fuse is a full size 20A blade-type fuse.

 

I looked at the wiring diagram, they show a main fuse @ the starter relay, then there are a lot of branches to that wiring before it serves the (2) fuses indicated at the fuse block.
Not the way I would have wired it, but that is the way it is indicated. Therefore any of those other branches could have shorted or overloaded and the secondary (2) fuse would not have blown.

Also if those are instantaneous fuses, if there is a short it would be difficult to predict which would have blown first. In the fuse world it is a big race to blow and the ampere of the fuse is not a good indicator of this blowing speed (where the fuses are of similar size). 10A & 20A fuses are a magnitude of 2X, but that is not a large difference in the fuse world.