The larger diameter wires are the primary and the smaller ones are the secondary. ignorance is not your friend when dealing with potentially lethal line AC. You should look at the transformer diagram on the side of the power transformer and compare that to the schematic in the mc76 manual so that you understand what you're doing. note that the PCB says 'orange' where you should actually put the red wire.
Yes, if you have an orange and yellow wire on your audio output transformer leftover, solder them together and insulate the connection with heatshrink or tape.
