the Ranchero disaster & Brand X update

Alrighty now (in my best Jim Cary voice)! let us look at the wiring mod I feel is necessary,
Here is the wire from the solenoid to the starter:

I'm adding a wire in place of the jumper, it may or may not be the issue that really is not an issue because the 'run on' is short and does not impact the flywheel, it's just a little annoying.
Here's what I have on hand:

the red wire on the left is likely 10 ga (or bigger)' I used to have a wire size guide but couldn't find it. The wire on the right is 12 ga automotive wire, the center is a roll of speaker wire , I like the idea of the 'duel' speaker wire that way when one burns out, and it WILL!! you have a backup wire already installed, so if the fire from the first wire didn't burn down the car the second can give it another chance
the question is 12ga the right size?
That red wire on the left has a couple sketchy spots so I can get more, oh, and other 'stuff:

I also have that 'special' tape in black so no more white 'special' tape.
Oh, and this antique:

Actually works quite good. An old friend gave it to me after he died, I know you're scratchen your head, "after he died"? how's that?
well he loaned it to me a few years back then died so now it's mine so remember that when one of you guy's loan me things, don't die till you get it back.
So let me know what ya'll recommend for wire size, anybody know what size the factory wire is and do I need a fuse or fuse able link on that wire? I'm patiently waiting