The Mainline north from Cagliari.
The project - authorised in 1981, as part of a larger programme of works for the FS - was for electrification of the mainline from Cagliari to Oristano, Olbia and Golfo Aranci; and the branch to Sassari and Porto Torres; also including significant upgrade works - double tracking, etc. It was, to a significant extent, to get Italian industry into the 25kV 50Hz game, and included (in 1983) an order for 25 locos (classes E491 & E492).
If I recall correctly, the first bit of the line from Cagliari was 'fully' electrified (at least at first glance) , to (I think) Decimomannu, and beyond there to Sanluri with only the main track wired through stations. At least some of the electric locos were shipped over to Sardinia, and ran trials from 1989 (some earlier trials had been run on the mainland, between Civitavecchia and Aurelia, on stretch of line suitably equipped for these).
There was something of scandal over the project (as a waste of public money - one of many such at the time), with legal investigations, before it was eventually cancelled in the early 1990s. Attempts were made to interest the French, or others, into taking the locos, but nothing came of these.
So that was a never quite electrified line.
But elsewhere in (mainland) Italy there are/were I believe a number of electrified lines, both FS and not, that were electrified, but either de-electrified or closed, over the year, but I don't know details.