There should be a resister originally mounted on the backside of the instrument panel,  This would be located up by the voltage gauge backside. This where the key switch wires are connected. There are 3 terminals with 2 on top and 1 lower.  Put 1 key wire on the top left terminal and the other on the lower terminal.  Check for continuety on those 2 post with key turned on. If no continuety, replace thst resisterl.  This is one of the easiest place to start.  I would recommend getting a shop manual ITF04.  These shop manuals have all of the part numbers with a great blowup of all the parts on the 8,2, and 9n's.  Wiring diagrams are in there as well.  I got mine from Tractoropolis.com. and they are around $36.00 plus shipping.

I have a 9N that starts, runs, moves, but the engine misses.  What is the best way to go about isolating and solving the problem?

Maybe list your solution in finding the problem in order.
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Thanks