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Primavera 4T 2014 150cc
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Hi,

I have an electrical problem with a Primavera VMA2T 1975. It's a 6V European model and it's repeatedly blowing out the tail, brake and pilot bulbs.

I have tried using all the bulbs according to spec, 5w for the tail and pilot bulb, 0.6W for the Speedo and 10W for the brake.

I've done some troubleshooting and it seems like the tail light is glowing really bright when the brake is not pressed. When the brake is pressed both dim to what I think is the brightness they should be considering they are 6v. When I measure AC voltage across the bulb at idle I get around 6V. When revving up halfway or so I get around 12V if I press the brake the voltage drops to around 6V again.

I thought the coil must be generating too much voltage so I replaced the coil with the blue and yellow wires but the problem persists.

I've been reading many threads on the issue to try and troubleshoot this but even though I have a good understanding of electricity, my knowledge of balanced load systems is quite limited.

Any idea why this might be happening?

Posting a picture of the stator for reference.

Thanks,

Tonio
Forum member supplied image with no explanatory text
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Honestly, I've never been able to get a balanced AC system to work right, so I just convert them to regulated. Unless you're wanting a hardcore purist experience, I'd suggest going that route.

To your specific problem at hand, have you confirmed that you have a Normally Closed brake switch, and that it's properly grounded?
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All of the above.

I'd confirm the switch and make sure the pedal is wired correctly.
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bodgemaster
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Is this the wiring you're working with?

https://www.scooterhelp.com/electrics/wiring/VMA2.pdf

The 6V AC systems are notoriously finicky. Check that you don't have the tail light and brake light wires reversed. Also check to make sure that all of the connections are clean and making good contact.

After blowing countless bulbs I ended up putting this tiny regulator the taillight-speedo-pilot circuit. No lighting problems since.

https://www.treatland.tv/yamaha-FS1-6V-regulator-p/yamaha-fs1-6v-regulator.htm
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SoCalGuy, yes that's the wiring I'm using.

It feels like a missing ground. Will check the pedal for grounding and confirm NC switch. But wouldn't the brake lights fail to work if there was a missing ground?
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Lucky
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it might be a bad ground, e.g. from corrosion, rather than a completely missing one.
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I've never had a balanced system work correctly for me either. Everyone says check the grounds but after years, that still has yet to solve it for me. Regulators have helped delay the inevitable switch to a new ignition system.

Definitely check your junction box, switch and bulb housing. If you still get nothing. Check for resistance between the blue and yellow wires. Those coils are wired together and are independent from the other lighting coils. If you don't get a resistance reading between the blue and yellow stator wires only, your coil is probably bad/stator wire bad.
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I forgot to add that this is a restoration project and all the electricals apart from the stator are new, including the wiring.

The yellow-blue coil is new. The circuit seems to be working correctly when the brake pedal is pressed. When it's depressed, there is over voltage on both the brake and the tail light circuits
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bodgemaster
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Get a regulator. I probably spent $50 on blown bulbs trying to chase down the same issue. The regulator solved everything.
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Does everyone have their lights on all the time? Just wondering if that would make a difference on a balanced system.

Mine kept on blowing the tail light but then we found the speedo bulb had gone and since replacing that, its been ok. - not that we're using it much at the moment.
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In today's world I would add an inexpensive Voltage regulator, 60 or 70 years ago system made since. A regulator does nothing unless voltage is to high then it shunts extra to ground and saves whatever it's connected to from being ruined.
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Thanks for your replies. I am aware that a regulator would solve the problem. However I am almost sure there is a problem with my wiring. Would I need two regulators for the tail/pilot and brake circuits?
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tlombardi wrote:
Thanks for your replies. I am aware that a regulator would solve the problem. However I am almost sure there is a problem with my wiring. Would I need two regulators for the tail/pilot and brake circuits?
I bonded my circuits together and changed out the normally-closed for a normally-open brake switch when I went to a regulator. Like SoCalGuy, I spent multiples of the cost of a regulator fighting the balanced system before I gave up and switched to modern tech.

Which harness are you using, since it's new?
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Quote:
Would I need two regulators for the tail/pilot and brake circuits?
I only regulated the taillight-speedo-pilot circuit (yellow wire) using the tiny regulator I linked to above. That solved the brake light (blue wire) issue too. Not 100% sure why, but I assume it's because they're both fed from the same coil.

As for your wiring, do you have a separate ground up in the headset? That's an important piece of the puzzle.
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What do you mean by a separate ground in the headset? I think, according to the wiring diagram, it's a common ground throughout. however, I cannot find a way of testing continuity as everywhere you test in the circuit gives you a short circuit due to the coils. I cannot understand how the piaggio engineers made these bikes to work this way from an electrical point of view. it really doesn't make electrical sense.

In the meantime, I have tried a rectifier/regulator on the yellow wire which solves the overvoltage on the tail light. However the brake light doesn't work like that. The brake switch is normally closed (I tested it). So, I was thinking of putting the regulator on the yellow wire, changing the pedal switch to normally open and connecting the brake pedal to the regulator too. I am assuming I would have to ground the blue wire on the coil in the stator (the coil with the blue/yellow wires). Does this make sense at all?

Thanks
SoCalGuy wrote:
I only regulated the taillight-speedo-pilot circuit (yellow wire) using the tiny regulator I linked to above. That solved the brake light (blue wire) issue too. Not 100% sure why, but I assume it's because they're both fed from the same coil.

As for your wiring, do you have a separate ground up in the headset? That's an important piece of the puzzle.
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Like Candlerman said below (read this after sorry)
chandlerman wrote:
I bonded my circuits together and changed out the normally-closed for a normally-open brake switch when I went to a regulator. Like SoCalGuy, I spent multiples of the cost of a regulator fighting the balanced system before I gave up and switched to modern tech.

Which harness are you using, since it's new?
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Can the brake switch be modified to normally open? Or does it have to be replaced?
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tlombardi wrote:
Can the brake switch be modified to normally open? Or does it have to be replaced?
It potentially *could* be modified, but it'd be a LOT of work compared to the price of just replacing it, where the shipping might exceed the cost of the switch.
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bodgemaster
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There's a ground to the frame at the taillight and another ground off the green coil that goes to the junction box up to the switch. Check that the No.1 connection at the switch is good. It wouldn't hurt to run another ground from either the pilot or headlight directly to a bolt inside the headset.
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That is revealing! Could a missing ground at the tail light end be causing this problem? I'm not using the original tail light bulb holder since it was missing. So I made one myself. But I did not ground it to the chassis...

But the speedometer is grounded through a bolt through the frame...

The ground on the green coil is there
SoCalGuy wrote:
There's a ground to the frame at the taillight and another ground off the green coil that goes to the junction box up to the switch. Check that the No.1 connection at the switch is good. It wouldn't hurt to run another ground from either the pilot or headlight directly to a bolt inside the headset.
⬆️    About 1 month elapsed    ⬇️
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Hi guys,

thanks for all your replies. I did not manage to solve this. After troubleshooting as far as I can go, I decided to replace the bulbs with 12V ones at the same wattage and the bulbs stopped blowing

Thanks for your help in understanding how these very rudimentary electrical systems work.

T
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I used the 12V bulb trick for a while when I was first working on my VBB. Even those would blow after WOT runs for me, though.

Definitely carry some spare bulbs and tools to replace them if you're going to be doing any significant riding.

I'm glad you have a fix that's working for you. Doing the full conversion is to 12V regulated isn't hard, but is a bit arcane.
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