Refrigerator light

Hi forum
I'm new here so thanks for being gentle.
I have trouble getting the light in my refrigerator to work as intended.
It has a simple light holder for a halogen bi-pin lamp, rated at 12v and 10w (using lamp base G4).
Seems to be all plain vanilla specs.
I've tried 3 different halogen lamps, all with correct rating. None work.
I checked all the lamps using benchtop power supply providing 12v DC and they do all work !
I checked the wiring in the refrigerator and it is delivering about ~ 18v DC into the lamp socket.
Is there a simple way I can add a resistor (or something else) into the circuit to get this working as desired ?
TIA's for any tips or clues.

Did you measure the voltage across the light bulb when it was supposed to be lit? What provides its DC voltage?
A 10W incandescent light bulb draws a surge up to 150W the moment it is turned on.

That 18V at the socket, without the bulb, is the open circuit voltage and it will drop when you add the lightbulb (a load). You have to measure the voltage with the bulb in place.
There appears to be AC and DC versions of those 10W bulbs as well. Are you sure you have the DC version? Most home 12V 10W halogen bulbs are AC (as in my desk lamp). While both will work with the same voltage and current, your power supply in the fridge may be seeing a different current surge on startup and shutting down perhaps?
Most DC halogen lamps are made for the automobile industry.