Modern Vespa

Hi, thanks for letting me join. I have a problem with the 10 amp fuse under the seat blowing. I've been riding this bike for the last 5 years with zero problems until one day it cut out just as I was getting home. Reading the manual it said check the fuse located under the seat, which I did and it started no problem. But, after riding less than half a mile, the fuse blows again. In summary; Engine starts and ticks over no problem. Go for a short ride fuse blows, replace fuse again blows (not instantly) Engine management light stays on. Checked battery, load relay and regulator and they all read okay. Jiggled wiring nothing. Any help to what to test would be very much appreciated.

stare the wiring diagram to workout what's on the same circuit to get inspiration

https://manuals.wotmeworry.org.uk/Vespa/GTS250/GTS250%20Wiring%20Diagram.pdf

Check the large brown electrical connector under the seat bucket close to the front of the bike. These are known failure points on the early GTS models. They have been known to start fires; so if it looks damaged in any way, stop riding and replace it immediately.

The 10A fuse just feeds the injection loads relay, and thereby the coil, injector and fuel pump. So either one of those things has shorted (uncommon) or wiring has become chafed and is intermittently shorting to chassis (quite common).

So check the wiring to and from the injection loads relay, under the seat on the left-hand side.

I've looked at the wiring diagram for the 10amp fuse and it protects
!. The HV Coil
2. Fuel injector
3. Fuel Pump
4. Lambda Sensor
What one of these would blow a fuse, once the engine warms up.

As above, it's more likely to be a wiring problem than one of the devices. But if you want a bet made, I'd go for the coil...

I do have this connector but looks okay, I'll test the continuality to make sure.

Thanks Jim,

What I don't understand is why it starts up and runs no problem cold but blows when it warms up.

That's why it's possibly the coil. If it has a heat-activated short in the primary, that'd blow the fuse.

It could be the Lambda sensor wire touching the exhaust as well.

All sorts of heat related scenarios are possible - but most are very unlikely.

Just give a very careful eyeball to those bits of the wiring.

Oh - it can't be anything to do with the big brown connector - but ensuring that is making good contact is an every-service check in my book.

Thanks Jim, I'm going to concentrate on the coil maybe heat from the exhaust is affecting it when it warms up.