That is a super- simplified diagram.
You'll notice it has no fuse protection for the ignition circuit.

Also, it does not show the alternator. The ignition voltage is most properly sourced from the main power distribution block, which also sources the sense wire to the alternator.

I read a really great article a while back which explained why the voltage works better that way (basically the alternator can accurately sense the voltage drop) but I have a habit of cleaning out old files, so I do no longer have the article.