'65 Dart - Is this a fusible link and what is the brown wire for?

Hello!

I'm starting to dig into the wiring of my '65 Dart (slant 6, 3 on the tree). The car runs well, but the wiring has clearly been hacked in several places, so I'm trying to replace questionable splices and to get the wiring the correct color so at least I know what I'm dealing with.

There's a heavy (10ga?) wire coming from the driver's side screw terminal on the bulkhead fitting (between the upper and lower socket) that connects to a 5/16 stud on what I believe is the starter relay, mounted on the firewall. Someone had spliced in a piece of blue wire with a wire nut and copious amounts of electrical tape, but the remaining part of the original wire is red. The ring terminal for that original wire (see pic) has a heavy black insulated section.

Question - Is that black section a fusible link? If so, does anyone know the amp rating?

Wrapped up with the original red wire in what appears to be factory electrical tape was another thick (10ga?) section of brown wire that was cut off at both ends.

Question - Can anyone tell me what that wire would have been for?

Thanks to all in advance for your help.

Chris