The zener will clip any positive spikes. If it is a negative going spike then the zener will simply conduct like any other diode. Either way it protects the LED.
-- We have failed to address the fundamental truth that endless growth is impossible in a finite world.
Now that you mentioned Masey-Fergeson, I know where the name came from. Masey-Fergeson is a name I've heard quite a bit, but most of what I've seen with that name is other farm machinery, such as balers, combines, hay mowers, etc. I'm guessing that Masey bought Fergeson, and combined the names. Your tractor must have been before that merge.
I kind of think that aside from the 3 major names JD, Intl, and Ford, the other lesser common brands are more regional, due to where they were made and sold.
I got a GMC truck that needs a rebuild for the same reason. Coolant in the oil. I'm looking for a different engine, seems easier to change it than rebuild it, but old tractors are a whole different matter, engines are not easy to find.
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