The switch that activates the interior light when I open the driver's door has failed (the one on the passenger door is fine). I have taken it out and cleaned the contacts to no avail.

Do I just have to buy a new one and, if so, how hard are they to source?

Hi,

According to Fiat Eper its part number 7673558

There are some listed on Ebay & Amazon, the cheap ones look a bit different not sure if its what under the rubber cover?

You might be able to get it cheaply from a Fiat Dealer it seems a common part.

I assume you've confirmed it is the switch by connecting the wires together

Thanks for the part number. Connecting the wires is something I should have thought of myself so thanks for this advice too.

switch from mk1 punto is the same . just search in a scrap yard !