Center roof light not working

Hi
I have my camper 2/3 years now and I've a few issues that need addressing (door hinges need replacing, roller window blind needs fixing, small ingress of water on toilet wall) but first on my list this winter is to get the center roof light working.
I've replaced the bulbs and the fuse(even though it didnt seem to be blown) and its still not working. I have a multimeter ordered and hopefully i can test if there is electric supply going to the fitting. Is this my next step or should i be looking elsewhere?

Its a 02 citroen granduca pegaso. Ya the other roof lights are working. The rear light is on a 10A fuse and the front light above the cab is on a 15A fuse. What im reading about cleaning a bulb terminal says remove fuses first to isolate the circuit. But which one? I suppose just take them both out? Anyone ever replaced one of these terminals?
Not getting much joy trying to get a read on the multimeter. Just blowing alot of bulbs and fuses trying to figure out the setting testing the live terminal