As said before, buy a proper appliance cord rated for 50 amps. It will have flexible stranded wire with ring connectors already installed. Install the matching 50 amp receptacle in the wall. If you don't have a box in the wall for the recep (which judging by the direct hookup of the feed wire you probaly don't) you can get a surface mounted "tombstone" receptacle that will attach to the wall or floor. Also replace the terminal block. Your problem stemmed from the improper use of romex being terminated under the lug. No way to get a good, tight, permanent connection, which causes resistance, which causes heat, which causes more resistance, which causes more heat, etc. etc. Fix this and all will be well again!

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1984 300TD 1981 240D