This picture shows the ballast resistor assembly, its connection from the high voltage power supply (the red/black/red wire to the left of the ballast resistor assembly), its connection to the plasma tube (the red wire to the right of the ballast resistor assembly), and the safety grounding clip to discharge the high voltage power supply's capacitors.
Note that the connection to the plasma tube goes through a hole in the plasma tube's left mounting tube. (Remember this picture is from the back.) The mounting tube's knurled compression ring can be seen just above the right-most (in this picture) pair of 11K/2W carbon composition resistors. This ring squeezes an o-ring in a triangular gland to firmly but gently clamp the plasma tube and its spacer in position.