i have a fiat stilo 1.4 16V active hatchback 5 door 2004 (04)
had lots of problems with water entering left rear light blowing bottom bulb (fog light/sidelight?)
just bought new rear light has bulbs but one is missing (fog/sidelight)
and the brake light has no double filament just single filament
am i right in thinking that the brake light should be double filament and the fog/sidelight single filament?
light setup is brake light at the top, indicator and reverse in the middle and fog/sidelight at bottom (4 bulbs in total)
thanks

I don't remember the setup, but the reason for the water is simple... When you (or someone else) have removed the cluster to change a bulb earlier, the bolts going into the plastic housing have been unscrewed a mm or two when the nut was removed. This prevents a watertight refit.

Take the cluster out and look at the 3 bolts. One of them might not be completely screwed in tight. This happened to me once, and actually flooded the spare wheel bay as a result after a week in the rain - in addition to a filled cluster. It got rather damp inside the car, and I could have goldfish in the light cluster.

I don't have fogs in that cluster, but on each side of the numberplate.

The rear light on the face lift models is Tail/Fog lamp, so is twin filament, and the top is the Stop lamp, so single filament.

So your setup is correct in the first place