I would think that the red washer is what holds the electrical contact in place that the bulb presses against when inserted. It also provides insulation of the electrical contact to the lamp. body The washer sits on a small spring. There may be a small slot through which to thread the wire.


Doug
2011 Plus 4 in Rich Maroon

1972 750 “ComDom” sprinter
1958 Triton 650
1992 Triumph Trophy 900