1974 Duster total electrical failure, followed by quick recovery.

If one side is the fusible link wire it might not be solderable.

Some wires, like the rheostat wire in the gas tank sender are a type of wire that does not solder properly.

Perhaps a higher amp capacity connector (weathertite) properly crimped on would be the ticket.

Another solution would be to take the plastic ends and drill them out to fit an inline splice to pass through.

Then put the connectors on the wires use the inline splice to join the wires, goop it up with clear silicone and slide the two connector ends together over the splice.

Once the silicone cures. It will look stock but be a permanent connection