After the cycle was complete and the food was taken out, after closing the door the inside light and fan would not shut off. Sometimes opening and closing the door a dozen times would make it quit. This finally did not work anymore and we left the door ajar.
I took it apart to investigate and found this model has three micro switches near the door latch. The one in the middle is for the heating portion, the other two are for either the fan and/or light (so research tells me).
Rather than mess around, I decide to replace all three switches at once. The microwave was built in 2004. I did not want to come back next month to replace a another one.
Only three tools needed (but unplug the unit first!). Use a Phillips screwdriver to remove the two screws that hold the long vent cover at the top of the microwave. Pull the cover off. Then remove the single Phillips head screw at the very top of the control panel. Move the control panel upward about 3/8 of an inch and it will then unlatch and you can let it pivot out toward you from its bottom edge. It will remain there like that.
You will need a 7/64" Allen wrench to remove the two flat head screws where the door latch meets the microwave body. Once those are out, you can move the door latch switch casing holder out of the microwave so you can get to the switches. You will need a very thin flat headed screwdriver to press over the little "ear" or "tab" that holds the switch in place (on left side of holder). The switch can be pulled out of the holder to the right once the tab is moved slightly out of the way.
The wire connector can now be pulled off of the old switch and pushed back onto the new switch. The switch and wires are then pushed back into the latch holder and that tab will snap into the little hole on the switch to prevent it from moving out of position. Repeat for the other two. NOTE: The top and bottom switches are the SAME so you need TWO of those (WB24X829). The middle switch is different ((WB24X830). Reverse the procedure to put things back together and that's it.
Our 13 year old microwave is now back in business. I was reluctant to buy a new one just for the cost of three switches. Once I knew what to expect, the actual replacement took 15 minutes. You can do this too!