Modern Vespa

LX150 starter stuck on even with key off. Have to disconnect battery. Just replaced starter switch, but still stuck on. Any ideas?

Likely the starter solenoid.

Yup, the starter relay contacts arc every time you turn off the starter - eventually they can either get so dirty they won't pass enough current (so just a click and then nothing) or they can weld themselves shut - which is what's happened to you. I've had several of both types in my time, so quite a 'normal' fault.

Replace the relay, or if you can open it up (some are glued closed) you can clean the contacts to keep you going until a replacement can be found.

Any auto store should have a suitable relay.

I believe I have this problem on my 2010 LX150

Tonight it started but the starter stayed on. Even with the key pulled out and in the off position.

Is this probably the starter relay contacts? I can't find any YouTube videos on how to get access to it?

Thanks in advance

Yup, that's the relay all right.

Open the seat, and remove the battery - be careful to remove the black negative wire first! The starter relay is the brown one one the right-hand side. It's held in quite tightly, you might need pliers to grab it and pull it up and out.

Usually they can be opened by prising the brown cover off. Prise the contacts apart, and very gently clean each side with a flat needle file.

Replace, and buy a new one right away!

Yup, you'll want to replace your starter relay. They can get stuck on, or simply fail to activate when you try to start your bike.

Make a note of the specs (voltage, amperage) and get something up to the job.

CPC/Farnell sell some good quality Japanese replacements if you're that way inclined. Else, just a replacement from your LBS or auto-parts store will do.

It'll look something like this (depending on the model):