What would cause this wire to burn up?

[4thgencreamsicle]

‘69 c10 sb w/points and no plans for hei as of right now.

I’m talking about the cloth covered resistive wire from the firewall that splits into the 2 yellow wires that head to the starter and coil respectively. No idea what that specific wire’s name is.

Went to crank it this afternoon and saw a small puff of smoke. It fried the 2 yellow wires from the crimp connection at the cloth covered wire all the way down. I saw in other threads how to go about replacing it, but right now I’m wondering why it happened in the first place. Ideas?