Hi all.

This is something I can help explain. It applies to almost anything electrical.

Current (amps) + resistance (bad connection) = heat (something burning or melting.)
This is not to say that the blower motor is not bad but does say that there is a bad connection in the fuse block. Fix the bad connection first, which in this case is to install the external fuse holder and fuse.
The sole purpose of the fuse is to protect the wiring in the system. If something shorts out then the fuse should blow to protect the wiring.
Please, please DON'T ever put in a higher amperage fuse then what is called for unless you want to burn the car up and possible total it. Believe me, I have seen many cases where a larger fuse was installed and the vehicle was either totaled or the bill was very high.

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84 500 SEL (307,xxx miles)