In my situation when I would turn on the defrost button, which heats rear window & mirrors, the electronic burn smell was very noticeable. Use the defrost for only a short time, less than 2 minutes.
When radio module does completely fry itself, it takes out the rear window defrost at the same time, but leaves the mirror heat intact.
The main problem was the thin wiring they used going into the modules. Over heat & melt was the overall wiring result. Some resorted to soldering in larger gauge wires, going into the new modules.