wiper harness

We are working on a 1973 Duster which had a 2 speed wiper motor. My brother changed his wiper motor and switch to a 3 speed set up. The 3 speed motor has 4 wires coming from the motor about 10 inches long to a 4 pin plug, two flat pins above and two directly below those. Is there another harness that would plug into that and the other end would plug into the junction block. I am not sure what the motor and switch are out of. Could it be he needs a specific 1973 Duster motor or are we just missing that adapter/extension harness. Thanks Bobby