Modern Vespa

Hello all

My GTS 300 has started to become impossible/difficult to start. I suspect that I have some sort of short somewhere but I don't know where to start to find it.

The bike sits with a battery maintainer on which claims about 13+ V charge on maintain setting. When it try and start the bike the dash lights flash. After a while of holding the starter button down it's starts to get a bit more juice and slowly turn the engine over until the engine starts to fire occasionally. Eventually it starts fully and idles quite well.

The video is of the starting sequence. -edit sorry can't work out how to get the video attached.



Any help much appreciated.



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first thought looking at that is battery

stick a multimeter on the battery before and while trying to start. (might take a 2nd set of hands unless you have clips on your leads)

test the battery.

just because it has the volts, doesn't mean it has the amps necessary to kick over the motor.

after that, then it's down the rabbit hole or up the diagnostic tree you go.

has this been a slow degradation, or did it present suddenly? what's the service history? how old is the battery?

The battery is 3 months old. I haven't ridden much as I have been away but kept the battery minder on.

The bike has been back on the road since last may (fresh battery). It has a usb port that I added as well as an alarm. Up until October it hadn't given me any trouble when the battery was completely dead.

Will get out the multimeter tomorrow and see what I can see. These batteries don't seem to survive being drained very well.

test the battery.

also, they don't like being drained much.

is the alarm OEM or an aftermarket. is the USB a light up doohickey? as in, do either of those draw anything even when the bike is off?

If the USB port is one that's powered when the engine is off, or ignition left on, then it won't take long to drain the battery to 50%, at which point it will have considerable trouble starting the engine. The typical ones on Amazon or Ebay draw about 40mA even with nothing attached. In four days you've used 1Ah. In three weeks you've used 5Ah, and the battery will not thank you.

The way to wire your own USB port is directly from the battery via a fuse and relay, with that relay coil powered from the output of the headlight relay.

Then it's only on when the engine is running, and if it goes faulty (very unusual) it'll only blow its own fuse and not stop the bike from working.

Greasy/Steelbytes & Jimc

I found my multimeter (its battery was dead too) and measured V and mA when the scooter is at rest. It measued 12.63 V and 0.13/0.12mA accross terminals without the scooter turned on.

I have another GTS 300 and it measured the same. Once I turned both bikes on though the Voltage accross the battery terminals dropped significantly more on the bike with the starting issue.

The USB port I have is one of the ones with the LED voltage display but it is installed on the switched supply wire from the standard alarm plug that comes off the wiring harness. When the ignition is off the LED goes off. I would have thought this stops it drawing current when the bike is off. As a precaution I have removed the + & - wires from the back of the USB port in case its the issue.

I concluded that I needed to get a new battery so got one and installed it. The bike will now start first kick. Once installed it gave 13.4V and 0.13mA accross the terminals with ingition off. Once I turned on the ignition the voltage dropped significantly by a few volts and wasnt stabilising (without the USB port connected). The other GTS dropped to about 0.5V less doing the same thing.

To give some more detail it has the SIP LED rear light kit and front/back LED turn signals as well as a Gemini alarm which as I understand are what the factory ones are.

Whats next? Do I need to pull each fuze one by one to work out which circuit is causing the big voltage draw? I have disconnected the new battery for now so I dont kill it too.

Many thanks

Don't measure mA across the battery. That's not the correct way to use the multimeter. You've probably blown a fuse in the meter -- but that's OK if it still measures voltage.

Does the other GTS have the same extras? If not, disconnect them one at a time until you find the culprit.

The way to measure the current draw is in series with the negative terminal and the negative wire. Disconnect the negative wire (NOT the positive), connect the meter between them on a 10A range to start with, and see what happens. Do NOT try to start the engine - but ignition on is OK.

^^^^

Exactly what jimc said

Thanks will do.

I took a look at my led rear indicators and it looks like the wires of the tail light indicator connector have rubbed through the insulation so this is the first place I'll test.

Diff between 2 bikes are :

Other bike:

2018 model is pretty much factory inc factory usb with a Piaggio alarm installed.

Problem bike:

2012 model ; Gemini alarm; usb port; sip LED tail lights and indicators.


I took off the rear LED kit yesterday when i noticed the chewed interconnect wires so can't now tell if there was a parasitic draw from a short there. I have made a new interconnect wire (it makes the indicators go red when not indicating) in case it was the cause.


I did the test as you describe , 10a slot for red wire on multimeter, negative cable off battery. Black wire to battery neg, red wire to neg cable and it's reading 0.001 A with ignition off. When I turn the ignition on it reads 1.8 amps

I am not getting the out of range or error signal from the multimeter. Could it be that a short in the LED wires after removing them and re wiring has now gone ?

I have done the test with the usb port connected and with the led lights plugged in. For now I am going to watch it and see if the problem returns. Anything else I should try?

The chewed wires would be an immediate suspect, so I'd wait and see.

are there any other wires on the black terminal or just the big fat one?

ie is the alarm directly wired to the battery? have you disconnected the alarm?

The alarm is wired into the standard alarm plug that sits behind the leg knee pad.

I didn't disconnect the alarm.

that alarm / accessories plug has a pin that is not switched, ie even when the ignition is off the alarm can still be draining the battery

There are 2 parts to the wiring, a section that is inserted into ignition circuit from memory where it gets its power from and the socket on lhs which is where the negative wire is. The usb uses the switched power wire of that socket.

If the draw is 0.001 A as measured is that indicating a parasitic draw with the alarm in place ( not on).

Did you ever get this mystery figured out?

It was 'probably' the chewed wires of the rear led interconnect. They had rubbed on the rear tyre.

I replaced the wiring and the bike is holding charge. I am going to keep an eye on voltages etc over next few weeks.