Modern Vespa

Hello everyone! bought recently mp3 400lt unfortunately it had charging problem so i found and replaced main fuse in starter solenoid. It didn't helped and bike start stalling and going on low revs only.

Bought new battery
I replaced voltage regulator still same issue
Replaced stator (as it gave me slightly lower voltage than it supposed to) without luck of repairing

After that i have found that when i disconnected main fuse it revs fine and it rides without problem but its ofcourse not charging

Replaced starter solenoid and all relays with new one
Cleaned most electrical contacts and looked for potential short on the cables but can't see any...

Replaced right hand switches
And now i feel powerless as i can't see what else it could be

I have cleaned throttle body and whole intake
Replaced oil and filters

Found out that it can be faulty seat sensor so i bypass it with 2.7k Ohm resistor and it still not working

Any idea where i should look next? Or is it piaggio dealers job only now?

Are you *sure* you checked the actual main fuse and not the spare, which is alongside it?

Checked the right one 100%. If the mp3 will work only with spare fuse out of holder that will be even more bizarre

Ah, I mis-read your post, sorry!

As this has been there since you acquired the bike, there may be something that a PO managed to mess up.

I'd be measuring the o/p of the new regulator while the main fuse is out, and the regulator is connected to the old battery. Some extra lash-up wiring required of course...

It's just possible both the old stator and the new regulator are faulty, but I'd be looking at the solenoid to check the wires are actually on the right spades. One or two bikes even made it out of the factory with that wrong.

Thanks will check that.
Any chance someone can provide me with photo of their selenoid connected to see colours of cables connected please?

Today i noticed that i have a bit weird noise from the engine when fuse is on and it is quite when fuse out. It sounds slightly like electric motor with constant power

Do you guys think that starter motor working constantly is possible without loud grinding noise from enhine and can couse issue with low revs with main fuse in?

What exactly is main fuse protecting and where its after fuse side goes to

Appreciate all help

I think you've nailed it. Get those wires in the correct place!

Yes, the wires are backwards on the starter relay. If the wires are backwards, the charging circuit goes directly to the starter motor, and causes it to spin when the generator system works (bike is running). That's the electrical noise you hear. Swap those terminals!

Cables swapped but they burn main fuse instantly. I have managed to dopower draw check on the fuses and can see that i have bigges draw on fuse number 5 (fuel pump, ignition coil, injector and radiator fan relay) so I think problem lays there.

Is there anyone here who can check how many Amp their fuse number 5 draw? I have almost 4 amps on there where rest of them is all under 1amp

Long shot - have you checked the solenoid hasn't welded its contacts shut? This is quite a common thing to happen on the smaller 80/90A relays used in Vespas and some other Piaggio bikes - but I've not heard of this happening to an MP3 so far. However, it IS a possibility.

Replaced selenoid doing same thing unfortunately. I belive that my ecu is having problems as soon as it gets power above 12.5 volt... no other way to check it than visit at piaggio dealer i believe

ECU changed today without results... still same problem.

Any more ideas what that could be?

Oh, that sucks and I am sorry to hear it.

I am also sorry I don't have any concrete advice for you.

But I am curious... you mentioned that reversing (correcting) the cables on the starter relay triggered a short circuit / immediate fuse burnout. Did you ever get to the bottom of this? How are you running it now (i.e. did you reverse it back to the "incorrect" wiring setup)?

I think it was wired correctly at first. I can not find anything what can couse the problem. Already changed most of suspected electrical acomponents and visually checked wiring loom. Can't see fault there. All the components giving right measurements on the multimeter. I cant ride it atm as it has no charging, splutters and shoots from exhaust without fuse and it dies as soon as you put fuse in... since i bought it i have ride it twice and already put lots of money in repair attempts...

Im quite handy with tools, been working on cars a lot, got some experience with electrics and electronics as im an electrician by trade. I had a friend who does repair bikes like bmw, triumph and harleys look at it and helping me with checkouts but even he can not see how this can happen...

I suspect bad wire somewhere but can't see anything obvious

Booked visit at dealer on next Wednesday hope they will have more clear answer what is going on there after checking obd

So what was the outcome?

Bike still at the dealers. No information yet as last time i called them it still wasn't checked. Or they struggling to find it... have to wait for the call. They probably not working full hours due to lock down