Modern Vespa

The battery on my 2018 Piaggio Liberty has been dying on my work commute and leaving me stranded. I ran a series of electrical tests on the the stator and voltage regulator (battery tested good, but bought a new Yuasa battery anyway).

Unplugged voltage regulator and

1) All 3 yellow wire combinations > 20 VAC at idle and > 50 VAC when revved
2) 0.6 ohms on all 3 yellow combinations with motor off
3) With engine off, test resistance between all 3 yellow wires to chassis ground. Measured OL (no shorts).

With voltage regulator plugged in and motor running

1) black/red wire under 14 VDC. Usually < 13.3 VDC and sometimes even < 12

I thought the regulator circuit was bad so ordered a new voltage regulator but the problem did not resolve. I swapped the newly purchased voltage regulator in my 2003 Piaggio LT150 and immediately measured > 14 VDC at idle. I even tested the "bad" voltage regulator in my LT150 and again immediately measured > 14 VDC and lastly installed the 20 y/o voltage regulator from the LT150 into my 2018 Liberty and again < 13.3 VDC.

I noticed the connector would get very hot and thought maybe my 2018 stator charges strongly so it was normal. Using the IR camera on my FLIR meter I could see only the black wire would get over 200 degree F and that side of the plastic wiring harness would get very hot. I had a nagging feeling that something is drawing current and pulling down the system voltage below 14 VDC and slowly discharging the battery while riding. I still wondered if the stator is shorted and that is why the black wire is so much higher temp than the other wires, but my previous test indicated no stator short to chassis ground.

I came across another test - with engine running and voltage regulator unplugged, measure AC voltage from any/all 3 yellow wires to chassis ground. There should be no measurable AC voltage? I measured 12 VAC which I believe indicates the stator is shorted to ground but only when running. I tested both using only the wiring harness and between chassis ground and the yellow wires. I can't understand why the stator won't measure a short with engine off but will only when the cold engine is running.

My question is if this is a valid test, and if yes, any helpful posts or videos on removing the stator on a 3V 150cc engine? I bought the workshop manual but it's pretty terse on that section.

Update - this morning I repeated this test on my 2003 Piaggio LT150 and also measured AC voltage from the yellow wires to ground with the voltage regulator disconnected and engine running, so this test does not indicate a short in the stator. I did notice the black wire did not get hot on the LT150 harness. Not sure what the next steps are other than start shooting the parts canon or take it to a Vespa dealer (at $165/hour shop rate).

What does the service manual show for stator testing. Are the coils to the yellow lighting wires grounded to the plate, or insulated?

What runs off the battery and what runs off the stator on the LT150? Headlight off stator but brake, tail, turns and horn off the battery?

The service manual is pretty terse on the stator and voltage regulator test, and being able to swap parts with a known working scooter at least rules out the voltage regulator and battery. I don't think I can swap stators.

As long as the motors turning, it's creating AC voltage!

The phrase, check that there's insulation between yellow and ground leads me to believe that the coils are insulated from the stator plate and engine case. When you did the resistance test between yellow wires, was that with the stator unplugged? If not, unplug and test the yellow wires to ground.

After that, my next step would be to focus on the DC circuits. At idle you said was 14V DC, does that get any higher with RPMs?

Sorry, I removed the stator just to visually inspect it. Is there a set of recommended tests on the stator when removed?