I seem to remember discussing a theory about the completely blank panel, it allowed a replacement standard headlamp to be fitted to an early machine with the switch panel in the tank.
it seems that the test (test-off-T-H) switch under the seat i have is working the same way as a 4 position (off-T L H) switch would that is fitted in the headlamp, im thinking mine has the wrong switch cam fitted, im trying to find a picture of one to se what it should look like,