Modern Vespa

Bought Vehicode LED bulbs for front indicator lights on Amazon. Work great. The rear indicator lights have a different base (Ba15s)but bought led bulbs also under Vehicode label to fit. Bulbs didn't light. By chance I tried an external 12v power source and tried switching the polarity. Both lights worked well. I suppose I could rewire the rear lights and make it work but don't want to. Do I just order a different brand and hope the polarity is right?

I wonder if Vehicode has the same bulbs with opposite polarity under a different part number?

The other possibility is that Piaggio did wire the bulbs with the reverse of the usual polarity (tip positive, base negative). Something like this situation:
https://www.taninautoelectronix.com/product/ba9s-led-with-reverse-polarity/
If that's the case you're probably better off to just rewire the socket, if possible.

Can you tell, with your external power source, whether the base is the negative or positive terminal of the bulb?

So, the led bulb works with positive at the top and negative on the base.

That seems standard and suggest the Vespa is non standard. I don't get that.

I have a multimeter but not sure how to check polarity. But I would think that if I ground the black multimeter lead, then just one side of the bulb socket will show the 12 volts. Right? Then I know it's polarity

To test for polarity with a digital multimeter, put the red lead on the center terminal of the socket and the black lead on the base. Then if the meter reads positive ("12.00") the red lead points to the positive. If meter reads negative ("-12.00") the red lead points to the negative.

I had no problems with polarity when installing led indicator bulbs for front and rear on my 2019 supertech.

https://modernvespa.com/forum/post2569440#2569440

Just flip your battery terminals around. You'll no longer have any more worries about indicator polarity.


No, don't do that.

I'm having a hard time believing that Piaggio reversed the "negative ground" convention on only one set of indicators on one model of Vespa scooter. It just doesn't make sense. Pending what Bill finds with his multimeter regarding the polarity — I would start looking for other causes. Are the bulbs the correct type? The LED version is fitting in the socket correctly? Broken wire? Etc.

This is complicated to me.

1. At first I forgot indicator circuitry is tricky. Remember what happens when one bulb burns a filament? The other bulb stops flashing. I guess that is a safety factor.
2. My front new LED bulb works but makes all the bulbs hyper flash. Not sure what effect that has on the circuit. I know how to fix hyper flash with a LED relay which is ordered.
3.both front and rear sockets work and both read negative at the bulb tip! Hard to believe I know.
4. The OEM analogue bulbs work whether positive or negative at the tip.
5. The LED bulb which works will work whether positive or negative at the tip.
6. The led bulb which does not work, only lights with positive at the tip.
7. The front working led bulb has the offset pins in the base which fits the front bulb socket but not the rear.

Conclusion: find a bulb like the front one with the proper base or file one of the pins on the front type bulb and get it to fit in the rear base.

Any questions or suggestions. Clear as mud, I know.

If it were mine I would just go back to the incandescent bulbs and be done with it. Rewiring the sockets for LEDs just isn't worth the bother.

It's not a bad idea. I'm too stubborn so far to give up!

Are there one or two wires going to each of the indicator sockets? Are there connectors in line with the socket wiring?

Yes two wires at rear. No connectors close. Cable goes to other indicator and to the brake/DRL.

In each pair of wires is a black wire and one with color. Left rear is solid pink and right rear is white with blue stripe. Now for the big confirmation. The pink wire and white with blue stripe both attach to the side of the bulb. The black wire in both, attaches to the connector tip of the bulb. I'll be darned!

I took a quick look at the schematic here. Looks like the wires to the left indicators are pink (Ro) and black (Ne), and the right are blue/white (BiBl) and black (Ne). I'd say you could cut the wires and swap them, but only if they go to the bulb sockets alone. There are some other devices on these wires (tail light, USB, horn, etc) and you risk messing things up if you cut the wires at the wrong places. Personally, I'd just go back to the incandescents.

https://manuals.wotmeworry.org.uk/Vespa/GTS%20300i%20HPE/GTS300%20HPE%20E5%20Wiring%20Sei%20Giorni%201Q000844.pdf

Thanks again JKJ. Your words confirm what I just added to my post. I'm still amazed that the black wires go to the contact point at the tip of the bulb.

I don't want to change the wiring because I'll forget I did it and a future owner won't know.

I'll take one more stab at a polarity neutral LED bulb.

Further, I have an Admore light bar I will install at the rear. The flowing indicator lights on it are so bright, the OEM indicators are almost irrelevant.

Also thanks for asking me if there were two wires. That made me check where the two wires go to on the bulb socket.

Back in the old days, automobile lights often had a single wire (the positive side) wired to the center of the socket, and the shell, or base, was directly, mechanically connected to the steel vehicle body (chassis ground). If your Vespa was this way it could really be a mess trying to isolate and swap the positive and negative sides!

That would be faulty - the other bulb and the dashboard tally should flash at double speed. That's as expected - see above. The LED looks like a high impedance to the flasher circuit (just like a blown bulb) so the flasher goes double speed Re-wire them. Luigi got it wrong. Just re-wire the 'bad' sockets. All bulbs will then work, along with an LED flasher. You could use load resistors instead, but that's a waste of money IMHO.

Jim, you are saying my indicator lights with non-standard polarity is a manufacturing error?

I wonder if the local dealer would rewire them under warranty?

I could easily do it, I'm just amazed such an error could occur on all four lights. And the lights work because the bulbs are not affected by reversed polarity.

Has anyone ever see or heard of this before. I wouldn't have discovered it if I wasn't trying to switch bulbs to LED.

Does Vespa publish a service log of known defaults? Thanks.

Don't go near the dealer, just re-wire them. Especially if they have push-on (spade) connectors.

I installed LED bulbs in the rear indicator lights. The bulbs are the same as those which worked in the front. Since the base in the rear requires different pins, I filed one of the pins about in half and that allowed it to fit. The bulbs worked in spite of me not having rewired them. I knew these bulbs worked with reverse polarity, so I went that way.

The LED lights and the Admore Light Bar are a blaze of glory to me.
The light bar automatically flashes my brake lights during engine braking as an added bonus.
I know not everyone agrees.

Tomorrow an LED Flasher relay will end rapid flash

Finally got the indicator lights, flasher relay and Admore light bar all working.
I'm happy with the result.