I'm still perplexed by the lack of a ground from the battery to the engine block.
I don't see how it would even start w/o that, let alone, run. You must have a fabulous contact between the engine and frame/body. Perhaps that's what you lost, and started the fire... but I don't see how that one would just come off. Mine is (was) helt on with a loop, bolt going through it on the motor mount.
is that bolt still there?

With 200+ Billion electrical parts, the world most complicated machine is inside your own skull.

Question Reality.
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'89 Rnr DLX "SR4.5", 32s w/ 5.29 locked f/r blah blah