Originally Posted by c107

You might very well have a switch that does not have a bulb socket.

Attached is a picture of the switch assembly, a real jigsaw puzzle to replace the wires.....

The bulb socket is the plastic section at the top of the switch.

As I mentioned I'm a little dubious that it actually works in our older cars.
I could just have the wrong bulb in there, but it seems to make good contact, and it's the same bulb used in many other places in the interior.

As you can see there's no way to get to any bulbs from behind. That "inner" set of connectors is covered by a plastic cover, I suppose to prevent accidental contact with anything from the "outer" set.

Steve