12 volt conversion

I’m having a few problems converting a Vespa Sportique to 12 volts (the scooter now has a 2003 px125 engine). I have wired everything in and it all seems to works fine until you press the horn and as soon as you press it you lose about 65% of the lights brightness. I have been working on this now for 2 weeks and have checked every earth and wire and they all seem fine but I just can’t seem to solve this little problem. Please help me any suggestions will be greatly appreciated.

how many watts are your headlight bulb?

Do you still have the 6 v horn?
if so, it will use 4 timers as much power on 12 v, i.e. if it uses 10 w on 6v, it will use 40 w on 12 v.

Hi ive left the explaination for this on the scooterboy world site but for anybody that doesn’t know: A normal px (non battery) has all the ac lights power go unregulated to the handlebar switch as a blue wire. It comes back down from the switch as the yellow wire to the regulator. It is designed like this so the lights don’t dim when the horn is pressed as it uses a fair amount of power(as has been noted). The gray wire coming from the regulator is regulated ac power for the lights. Older vespas had a seperate power source for the horn so that is how they work. The only way round it is to either live with it(as does every lammy owner with electronic convertions) or wire you horn to unregulated power from the stator. Make sure you use wire that can take the extra ampage though. Hope this helps.

no the horn is 12 volt

You’re not decking the -ve side of the horn to ground (chassis) as per a normal dc car setup are you? With a PX circuit the horn is ac and should be wired in series with the lights.


no the horn is 12 volts