This heat could have come from excess current draw due to a failing part, such as the magnetron, or an improper voltage level at the outlet. It should measure 105-125VAC.
A loose connection can also result in heat and melting.
I would recommend replacing the section of wire that's melted. You need to make a good solid connection with proper wire nuts and solid crimped connectors.
If you think the TCO may have been stressed, it should be replaced, too.
I would also check the fuse holder by seeing if you can twirl the fuse with your bare fingers while it's in the holder. If so, then it is too loose and the holder must be replaced.
You cannot just squeeze it tighter with pliers, because metal fatigue will make it go loose again, possibly resulting in a melted fuse.
Lastly, I would replace the primary interlock (top door switch). See http://www.microwavedisplay.com/doorsw.txt
Then make sure that no one opens the door while the oven is cooking unless it is specifically called for
in the cooking cycle. Opening the door while it is cooking leads to premature switch failure and heat / melting of the switches connectors and wiring.
You can find the full service manual online here
Yours may have the revised circuit. You can see the "mini-manual" for that version here
.There should also be a "mini-manual" hidden inside the unit behind the control
panel or hidden on the left side behind the grille, which is very
helpful when troubleshooting, & testing.
our Web site, we have a video available showing how to remove a typical
over the range control panel assembly in under 5 minutes.
You can find
links to helpful exploded view diagrams and part ordering help
I'd recommend that your bookmark this link to your favorites.We're
happy to help you with free advice and we'd appreciate your thoughtful
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