First ordered line fuse. After replacing, breaker tripped immediately indicating a short somewhere. Using the servicing guidance located inside the microwave, I used a multi-meter to test each component. Problem ended up being one of the three door micro-switches. Switch was supposed to be open when door was closed, but remained closed either way. Ordered switch and replaced. Problem solved.
Biggest obstacle was microwave was part of in-wall combination oven weighing 340 pounds. It had to be completely removed from wall.