First thing I'd check would be the fuse. I think it's the middle one; it should say Heater or maybe ACC. If it's not the fuse, then it could possible be the resistor on top of the heater box but I'd first check the fuse. Just dieing I'd suspect the fuse.
I thought 1966 moved the wiper motor into the engine bay. If true, I would be surprised if the same PN as earlier cars. Anyway, I agree on checking it first. Can't you apply 12 V easily w/ jumper clips or measure what voltage is at the motor?