interior Refrigerator Light not working

The light went out so I replaced the bulb on the interior. I suspect it has never been replaced. Now, it still does not turn on when i open the door. How do i troubleshoot what is wrong? It is an old Whirlpool- Mark Series, but the refrigerator is still working. thanks for any advice to be able to see the food inside again.

Check the light switch and the light socket.

Here are the breakdown diagrams for Whirlpool refrigerator [MODEL]ET20MKXPWR0[/MODEL]

Gene.