Well, this sketch will just send the same thing over and over. That is why the Tx light stays lit all the time. And you will need to have the relay board connected to dig 0 and dig 1 (Rx Tx) to talk to the relay board. I think you also need to set relay_address1 = to whatever address you have the board setup for. You may also want to add a delay() between the messages so you are not bombarding the relay board with messages.