That is a late 60's rear defogger sub harness. The dual terminal started at the kick panel and the single end connected to the defogger motor on the package tray. The was also an adapter harness that picked up the power for the two speed (Off, Low, High) speed switch that had a break off that went from the dash switch down to the kick panel. The early versions used two different wire gauges connected together underneath the part number tag. With the white wire being 20 gauge and the black wire being 18 gauge. The smaller gauge white wire was the Low speed and the black 18 gauge wire was the High speed. This was done through 70. The 71+ rear defogger harness changed and was now using a resistor circuit board mounted on the defogger housing, just like the resistor circuit board used on a non a/c heater box. So two 18 gauge wires from the kick panel made it all the way to the defogger motor.
Jim
