Modern Vespa

When I'm driving along I can see the headlight flicker super-bright occasionally, especially at high rev's and when I go over a bump. In the past week I've blown two headlights and just today the left indicator lights.

Can someone help with some assumptions...

Assumption 1) Headlights are AC and won't be blown by issues with the regulator (stop worrying about the regulator that I recently had installed because the old one wasn't charging the battery?)

Assumption 2) Bumps causing change in brightness isn't much of a clue either as you'd expect a short to cause dimming?

Assumption 3) The fact that they blow when I'm doing about 70kmph/45mph is a key clue. (I just don't know what it suggests!?!).

Any help would be appreciated. Cheers.

If this wasn't happening before then it definitely has something to do with the part installed or bad installation.


A short on before the fixture can cause dimming, and after can cause the bulb to fail.

If it happens at higher RPMs when the engine is putting out more juice then you definitely have a regulator problem.

If your light gets momentarily brighter limmediate after hitting a bump it is because your back tire comes off ground for a split second and the engine spins faster because of it and then there is more electicity being generated. Or some wires are slapping together.

IIRC the US model P had the headlight running through the regulator but separate from the battery. I think it's AC but is clipped by the regulator to keep the voltage from going too high.

Not sure if the PX was the same.

Going to edge my bets here because you can never be sure of history and type.

The regulator is either loose or the earth wire is.

They work by dumping excessive voltage to the frame... If its the type that use's the regulator case or a metal strip on rear make sure its tight to frame. others use an earth lead, again make sure its not loose..


I suspect when you go over bump in road the required earth is lost resulting in over voltage.

I agree it is likely to be a regulator problem. My Vespa has no battery and blew bulbs as soon as you revved it up. Rather than replace the alternator windings I decided to get an AC regulator from Ebay and the problem has been solved.
Of course with a battery it's all rather different. The battery acts as a regulator itself and anything powered by the battery should be OK.

Thanks for the suggestions - much appreciated.

This is actually the second regulator I've tried (first issue was that the battery was not charging, which it is now). Both have been second hand - I'd be unlucky but I can see how the evidence points this way.

I'll review the installation and make sure it's grounding well either via the connection or mounting to the frame. I'll also look broader into the wiring to/from the regulator to see if anything is defeating it given that I've tried more than one regulator.

oopsclunkthud - is that the difference in setup between the five pin regulator and three pin regulator setup? Will be interested to see what's on the bike.

Thanks again, I'll let you know how I get on. (10 month baby old says this will take me about a week if you know what I mean)

Loose ground or regulator not regulating this giving voltage surge.

Just went over the whole setup, tightened connectors, de-rusted screws, scraped away paint and dirt. There was nothing really obvious wrong but I've a few spare bulbs and I'll see how the next few days go.

If I blow another under the same conditions I'll re-re-replace the regulator! (5-pin btw)

Had same problem crop up a few months ago. It started after I had removed the stator to replace the flywheel side seal.

First step- pulled stator back off- found that 2 wires had broken due to age- couldn't handle the movement of taking stator off- Replaced two wires. Still had problem.

Found fuse blown in the rather crusty fuse assembly on battery side. Clean connections and replaced fuse- Still had problem.

Decided I couldn't justify any more blown headlights so ordered and replaced the regulator. Bada bing. Problem fixed.

No idea if this was a cause and effect issue. Presumably my regulator was just fine before I started the work to fix the seal, since my headlight did not blow prior. I wonder if the broken stator wire somehow caused a short or similar that resulted in the 30 year old regulator to give up the ghost....

Hey, Blew a bunch more bulbs... actually most went a little above idling speed. I talked to a local mechanic who interestingly said that this was no surprise as this is the time when the engine produces the most excess power - at higher speeds/rev's the spark plug tends to draw off a lot of power.

Setting that aside, I ordered a new Piaggio regulator and went to install it and came across two issues. I could do with some advice before I go and ruin the perfectly good new one!

Firstly - the existing regulator is G, G, B+, C, Gnd and the new one is A, A, G, B+, Gnd (which matches the wiring diagram). Would this in itself point to the reason I've been blowing bulbs? Incorrect regulator?

Next - I had to decide how to connect up the new one. Unfortunately the wiring colour coding on the bike bares no relation to the wiring diagram so logic told me G=A, G=A, B+=B+, C=G, Gnd.=Gnd. At a guess my thoughts were that A and G were the same (D/C outputs), C/G are the power from the stator, B+=B+ and goes to the flasher and ground is ground. HOWEVER - the attached photo shows my issue - there is a connection (red arrow) to the flasher that is coming from G not B+!! - are these to the indicators and all are wired to the wrong pin?? So is the wiring in the bike wrong, could this cause the blowing of the bulbs??

Thanks in advance, hope I'm not being too much of a newbie and this 'case' has some merit!

Firstly the ignition circuit is seperate from the lighting so what the spark plug does has no affect on this.
The rectifier you need will depend on the stator fitted, as you have no yellow I presume that your stator is a five wire type with a blue lighting output wire (check this). If so, for this stator the G,G,+B, C reg is the correct one, (an A,A, B+, C needs a 7 wire type). The 2 "G"s are the AC reg connections, so looking at your wiring you have an AC indicator system (flash alternate front to back).
To test the reg you have, remove the green and grey wires from the second G connector. Make up a test rig using a headlight lamp + 2 wires and connect between the vacant G and the reg casing. Start and rev the scoot, if the lamp blows your reg is faulty.

Getting ready to go over your recommendations firekdp (thanks for the feedback, you sound like you have a fair bit of experience).

Just thinking of my options - since I have the second (incorrect) regulator, could I use this in series to regulate the power to the headlights? Would this be a case of routing the blue headlight wire through the A-A terminals on the second regulator and connecting it's ground to the frame?

Yes, if the original is proved to be dud, take the blue stator wire to one "A" and connect the other "A" to the "G" on the original reg. Make sure that the new reg is earthed. This will actually put the new reg in parallel with the old one.
Make sure that the DC part of the old one is still functioning correctly by measuring the voltage across the battery whilst revving the scoot.

Ps. Although it would be easier to fit one correct reg/rec. LOL

Thanks Firekdp. That's good news!

Parallel? - series surely? (sorry I'm a mech engineer, never can seem to get this stuff right!) The way you describe it I envisage the power from the stator coming through the new regulator first, dumping excess voltage to ground and then through the old one? I'll read this again tomorrow with the diagrams out - I'm sure you're right. I'll give it a go anyhow.

I should indeed just fork out for the right one - but I really just need to get the bike on the road as soon as possible to see me through the winter months. When the summer comes round I can set things straight.

Thanks again.

No, the "G"s on the old one (and the "A"s on the new one) are shorted together inside the unit. The regulator part is connected between this and the earth connection and therefore in parallel with all other loads. This is why the earth connection is so important, without it the regulator isn't in circuit.

The simplest way to ensure that you do not blow your headlight out at high revs is to install a generic ac voltage regulator behind the headlight. Check dennis kirk or any other motorcycle supply place, they should offer a MSR or Tucker Rocky Voltage Regulator. Although the best one is the TRail Tech one.. it's only $19 and is adjustable.

Here is a link;

http://www.motosport.com/dirtbike/TRAIL-TECH-AC-VOLTAGE-REGULATOR

If you want to replace the ducati style regulator at the battery then I highly suggest one of the GY6 regulators;
http://www.scooterdomain.com/GY6_Gas_Scooter_Parts_p/gy6rl302359.htm

Right, just to tie this off for the moment.

I wired up the second regulator as suggested. It's not blowing bulbs and I'm the somewhat unlikely victim of three bad reglators in a row!

If it works it works - come summer if I have time I'll fit a new (and correct type) of regulator.

Thanks for all your help.
m