Why do we do this?
A common though sometimes unspoken question in this
field cabbage patch of human endeavor...
Minda switch wire colors - on my fairly recent example the wires are mostly routed into plastic 2.8mm terminal connector blocks:
In the 2 way green connector Blue = dipswitch to headlamp main beam, Green = dipswitch to dipped beam;
In the 4 way black connector Grey = speedo and tail light supply, Grey and Black = pilot/side light supply, Purple = horn to horn (earthing) button, White = supply to indicator switch the from flasher/blinker unit;
In the 4 way green connector unit, Red and White = the power supply to the switch from the ammeter, Blue = main beam warning light. (plain) Yellow would normally be the AC supply to the headlamp. For use in an all DC set-up it needs a 12V feed off the ammeter and can be combined with one to the Red and White wire, Yellow and Red = DO NOT USE OR CONNECT TO ANYTHING on a DC system;
That just leaves the two with the 3.9mm bullet ends. Black and White wire = indicator switch to left-hand indicators and Black and Green wire = indicator switch to right-hand indicators.
Hope this is helpful.
A.