And now for something completely different but this uses electricity so thought I would add it here; Front lights stopped working on a 2001 Aprilia Leonardo 125 (ST). The fix worked out to be rather easy: There is no relay with this – it is wired from an ignition supply through the right-hand light selector to the left-hand high/low beam switch and then down to the headlights.
To test this you need to remove the back of the display console like you would do to top up the brake fluid (i.e. you would have to remove your windsheild/windscreen as well if you have one).
If you look inside where the right-hand side controls are you have the starter motor switch on the bottom and the light selector above it. The Light selector is in two parts each with 3 pins; the top of the switch is the main lights and the bottom is the back and front side light (which is a small light in the middle of the front light cluster). For the main beam section it has a green supply wire and a black/yellow wire that goes across to the left hand side high-low beam selector. There will be regional variations with this switch but they should function the same.
With the ignition on then you should get 12 Volts on the green supply wires and when the switch is moved to the on position then the 12V should appear on the other pin.
With mine it wasn’t so I remove the switch; to do this there are on the back, a tab on each side of the switch towards the top which you need small flat screwdriver to push in and so can now push the switch out. The switch comes out and up as a complete assembly.
There may be newer models that are all sealed but with mine the dismantle was easy – on the back of the switch there is a section that pops down and you can now take out the inner red spacer and then slide out the switch lever. My fault was obvious; over time the switch has heated up and the plastic of the switch has melted and has stopped the switch contact from staying in contact. Cleaned out plastic with a knife, bit of plain grease, reassembled, tested and installed and the lights worked.
Second hand (or even new) this part is quite cheap so why bother with a repair ? The problem is that the bike isn’t street legal without lights so if it can be fixed without having to hunt for replacement parts then your downtime is reduced. While you are at it, if it hasn’t been done, you can do your brake maintenance given you have the master-cylinders exposed.