After looking up on the computer a schematic of the unit, all that was needed was removing four screws to remove the top and side cover which was one piece. Next was removal of electrical connection to burned out lamp, then removing burned out lamp and installing the new lamp and reconnecting electrical connection. Job was complete after reinstalling the cover.
Microwave now working with new lamp lighting when in use.
Continuity checks showed the flame sensor was open. Schematic notes it opens at 217 degrees and closes at 30 degrees. Removed sensor and placed in freezer for twenty minutes. Tested sensor and it was now closed, reinstalled and microwave worked normally. Ordered new sensor in case the original is operating at too low a temperature.
First I ordered and replaced the diode. That did not help. Then I ordered both the magnetron and the thermostat magnetron because I didn't know what I was doing. After I replaced those, it still wouldn't heat. So I called an electrician. He noticed I had knocked a wire loose. I connected it and the microwave worked. I reconnected the old magnetron, just to test it. It didn't work. Then I put the new one back in. It's working just fine now! It took quite a while to put everything back in place because it was a built-in. But it was a lot cheaper than getting a new microwave, even with the cost of a repair man to show me I had a loose wire!
