There are three switches and a thermal fuse....Here is a wiring diagram...The problem is ...That once you have removed the cover you will need a meter to test for micro wave leakage..Not to mention the high voltage that is stored in the unit even unplugged....If it the door switches check out ok then i would have a qualified service center look at it or replace it..Here a bulletin you might be interested in...
Consumer Product Safety Commission
Electrocution Hazard with Do-It-Yourself Repairs of Microwave Ovens
CPSC Document #5061
The U. S. Consumer Product Safety Commission (CPSC) warns against do-it-yourself repairs of microwave ovens. Each year, on average, four people die from electrocution trying to repair their microwave ovens. Microwave ovens use high voltage which makes it particularly hazardous for consumers to remove the cover and touch electrical parts. The possibility for electrical shock from a microwave oven still exists even after the oven is disconnected from the power source. Should certain internal devices fail, even unplugged ovens can cause serious injury. The Commission strongly recommends that consumers have professionals repair microwave ovens because electrical appliances can be hazardous if consumers expose live electrical parts.
/!\ WARNING ELECTROCUTION HAZARD HIGH VOLTAGE Removing the cover of your microwave oven and touching an electrical part can kill you.