Thank you everyone, so much, for all your responses! It is wonderful to know that I am not all alone on the island of X-10 programming land. To answer some questions, I am using single-phase, 60Hz here in California. I have employed both 4.7K pull-up resistors to 5 volts, as specified in the MEL PBP manual, on the collectors outputs of the opto-isolators of the psc05. In the X-10pro diagram, they show an OEM box on the left and the psc05 on the right side of the rj-11 connection pins, but in the middle, they show the suggested interface circuitry, which includes a pnp transistor that serves as an inverter to the input of an opto-isolator in the psc05 (when base of pnp goes low, the transistor's collector pulls up to 5V, to source current wrt the led inside the opto-isolator). I am thinking that maybe everything is OK, electrically, but maybe I am just sending incorrect codes to activate anything in X-10 land. But, it did seem strange that psc05 led just seemed to dim and stay dimmed, rather than blinking off when valid X-10 codes were going across the link, as when I used a real X-10 remote to do that same job.