Product review (3 stars): Whirlpool dryer interior light stopped working
When my 6 year old Whirlpool dryer's interior light stopped working I installed  a replacement bulb - no joy.  A quick internet search indicated that the door dryer switch may have been the culprit but I did not think of it because I had not opened the dryer while running:  a broken switch will allow the clothes drum to continue to spin even though the door is open.  Sure enough, the switch no longer made a click when pressed and the drum still rotated while the dryer was on.  Diagnosis made, part ordered/received, 3 minute installation.  A YouTube search of "replace (Brand) dryer door switch" yielded a short video which walked me through replacing the part.  My dryer is the type where you remove two screws near the top lint screen, pop open the dryer top, pull off the plastic electrical coupling of the broken switch, remove two screws holding the switch and connect the new switch.  Problem easily solved without a service call.

EDIT:  This switch's small black plastic "tongue" broke almost a year to the day after installation.  Since the dryer is useless without it, I ordered two more from Amazon to have one as a spare.  Had the manufacturers made the tongue of something more durable like thin metal, there would not be this failure.  Downgraded my original rating to 3 stars because of this.