I called Whirlpool customer support and ordered the replacement bulb (part #4375348) $24 + $6 shipping. I thought this would be a simple little "honey-do" project, but it's anything but. Our unit is built into the wall and there's no way to get behind the unit. We started by removing the 2 side trims along the oven/microwave. We then removed the black plastic grill just above the microwave door. Then we were able to lift up the control panel above the microwave. This exposed a lot of wires, but the bulb is not exposed. The bulb is below a metal sheet which leads into the vent area (I believe). At this point we couldn't figure out how to get below the metal sheet into the vent area because some of the screws are in places where we can't get a screwdriver in. It seemed the only way was to dismantle the entire microwave/oven, and we thought better not to. We put everything back together again, and were glad everything still worked (except the light).

I don't want to spend $$$ to have a service person come out to change a light bulb. We could live w/o a microwave light, but thought I would post a question out here in case someone has success with replacing the microwave light and have words of wisdom for us.

Lily, July 2007

I suggest that consumers here in the USA form a coalition and sue the manufacturers of these newer model built ins. They are engineered to require maximum effort and cost to replace a simple light bulb. They are hoping to get consumers to buy their extended warranties by making simple upkeep impossible for the consumer.

John, December 2020

In all honesty, they're much more trouble than they are worth. I'd just live without it if I were you. Built in microwaves are the bain of service engineers lives!!
Lamps are a luxury, but cause more problems than you need when they blow.

Jon, July 2007