When I opened up the amp and tried to figure out how the previous owner had wired the bulb I must admit I became confused.  From the power cord outlet located on the back 3 white wires run from the two terminals (the ground is clear and easy to see where it goes).  However 3 wires run to the rocker switch on the front where there are only two terminals.  I'm sure this should be obvious but can someone tell me where each of the three wires connect.

If also notice a slight hum in the right channel and wonder if the wiring of the rocker switch (previously) may have been the cause.  If tries swapping tubes but the hum remains.

Thanks in advance for any help.