Modern Vespa

Its strange I have this light bar https://www.ebay.co.uk/itm/334882466595 which worked on LX125 2013 but on my 300 GTS 2017 it only works when the lights on the bike are disconnected. Weird. Any help appreciated. Thanks

How are you disconnecting the lights? Removing the +12V or the grounding to chassis?

And is the light bar connected in parallel with the other lights?

Hi

I'm disconnecting lights at the connectors. Then the light bar works for those lights disconnected. Example disconnect at right hand indicator then bar will light up and flash amber but no run light until I disconnect rear light cluster connector.

I'm using the ground wire to one of the indicators.

Should I just ground to the chassis?

Thanks

I'm assuming this is an ABS fitted GTS, but not an HPE, so I'm going by this wiring diagram: https://manuals.wotmeworry.org.uk/Vespa/GTS300-2015-ABS/GTS300-2015-ABS-wiring.pdf


The light bar should work as you'd expect, but check to see if the previous owner fitted LEDs instead of the OEM incandescent bulbs. If I've got the model right, only the front position lamps should be LEDs, and they're 12V ones, so no undefined resistors hiding in the wiring.

I'm using one of those LED light strips
Brake light on top of top box

Melt: Picture please! Would like to see how it looks on your bike!

On the LX 125 it looks like this.

On the GTS 300 I put in a similar position but it didn't want to work even when I soldered the connections. Got the right indicator to work but the rest would only work with the bulbs and /or connectors disconnected from bike. Totally annoying. So pulled it off and will rethink the issue.

What I did found out with my GTS is that the red wire to the rear indicator bulb was ground so maybe I have issues somewhere and this is causing issues with the light bar. I will have a think.....hmmmmmm

Ah yes - do NOT think that the wire going to the outside of the bulb is the negative - the incandescent bulbs work either way round, and Luigi at the factory won't have cared which way round the wires were connected.

The ground wire is always the black one on this Vespa, as per the circuit diagram referenced above.

Looking at what they cost, do you have one on each bike, or one you tried to switch from bike to bike? If it's one on each bike, I would switch the one you know works for the one that you are having problems with and see if that fixes the issue.

Good point about the original, but I did test the new light bar with a 12v supply before fitting and all functioned as it should do. But as you say maybe the product has issues. As jimc asked before how I fitted the light bar, it was in parallel maybe this one prefers being in series. I may test this in the future watch this space. Thanks

In parallel is what it should be.

But with the right polarity! Check with your multimeter...