[Flip]

Okay, I've just re-read this thread (I replied earlier using my phone and couldn't be bothered to read it all).

So you have 12v at the connector and the light comes on when you short the terminals suggesting the circuit there is good.

I think the photo Capo posted is from a later bike with an electric fuel pump hence the additional wiring and circuit board whereas the early bikes used the float only to make or break the circuit.

So a silly question- If you shake it does it rattle?

I know it seems unlikely but if you have three sensors all used and of the same rough age is it possible they could all be gummed up with years of crappy fuel.

I know Ducati have had quite a lot of stick over the years about dodgy sender units but personally my twenty one year old bike is still on the original but maybe it's an exception as it's also on the original Regulator/Rectifier too.