Aprilia Leonardo 125 loss of ignition due to faulty switch

On my Aprilia Leonardo 125 ST year 2001 scooter, about the same time that the starter motor was playing up, the ignition would fail. I initially thought this was all interrelated but it eventually stopped all together i.e. the dashboard lights would be off (no oil pressure light and no indicators) plus the headlights stayed off and the starter relay wasn’t working. It was dead.

I proved where this was quite easily once I had a multimeter. The 12 volt feed goes from the 20 amp fuse in the battery box through the wiring loom to the ignition switch. To get access to this you need to…

  1. remove the front fairing as if you were accessing the radiator
  2. remove the protective trim parts that are on the edges of the internal shield above the mats. These are held on by 3 large hex bolts
  3. loosen the front shield so that you can get inside the area behind the shield

The ignition key and switch is on the right hand side of the bike and has a long cable about 30 cms that goes to a plug. If you unplug that plug then you can test the switch operation. It is very simple on the 2001 model – no fancy electronics. The 12 Volt comes from the fuse, goes through the switch and back to the rest of the electrical system and the fuse box.

If you set the multimeter to continuity or resistance¬† then when they key is in the ignition on position then the switch should be closed and show a short i.e. zero ohms on that plug. Mine wasn’t – the switch wasn’t closing.

This switch is not easily field-repairable because the cables are soldered in the switch. If you want to get home then you need to simply short the socket that comes up from the wiring loom. This (in effect a “hot wire”) will work and you can get home or to a garage.

When you are home then you can inspect the ignition switch. It is in two parts – the key part which is fixed permanently to the frame and cannot easily be remove and the electrical switch part which is removable. There are two screws that hold on the plastic electrical switch but they are hard to reach. You will almost certainly have to unbolt the horn and move it up and aside to get room.

Note that you cannot use a screwdriver but must use a screw bit with adapter in a small (1/4″) ratchet wrench tool. If the radiator looks like it is in the way then it may have jumped out of its mounting – mine was (the rubber bush on the top was broken).

Once the switch is out then mark the position of the switch with a CD marker pen and pop it open. It has the usual plastic locking tabs that pop into holes so easy to carefully pull apart. What I found on mine was that the contact had heated up so much that one of the wires had un-soldered itself.

I carefully trimmed the wire and re-soldered it back into the hole. I then also sealed it in place with High Temperature Silicon sealant (red or orange) and then reassembled, screwed it back onto the ignition key switch, bolted the horn back into place and it is all working fine. Note that I initially had not used sealant and the other wire came lose about a year later. Ideally if you use sealant it should all stay in place.

I’ll post another post that brings the three problems I have had together i.e. headlamp switch faulty, starter commutator worn and ignition switch faulty as I think they are related to something that happened 6 months ago when the regulator failed.