Non Switchy offy cinquecento

What do you mean doesn't switch off? It acts as if the ignition key is in and turned to the last position and everything works or the engine just keeps running but, for example, the gauges on the dash stop working?

Ah sorry, I should have been more clear. The engine keeps running, but everything else seems to act as if the key has been removed i.e. the gauges and lights on the dash stop working. The battery light is illuminated though.

Well, if it was a lot older I'd say it needed a decoke..

Presumably it's a carburettor model? Injectors really ought to shut off when you take the key out.

You can kill it easily in a decokey sort of way: while stopped, dip the clutch, into 4th/5th, foot on the brake, bring up the clutch.

Stopped.

He's having to do just that. The OP is asking how to cure the problem. Mike.

I know that. I started with a suggestion...

Then I suggested how to cope with it while doing the least damage to the car. I've known people who just stall out of running on every time for months, and never bothered to fix it.

Nah, it's a injection.

I'm lazy, but I'd rather not give in and to resort to that :)