Following wiring harness applies for Ford tractor 9N and 2N series. Here you will find detail illustration of the electrical system, wire harness and electrical schematics diagram of the tractors. For the 12 volt conversion wiring diagram; if the original coil is used, a ballast resistor must be added in series with the coil to drop the 12V down to 6V. Herein you will find also brief description of the interconnection between the electrical parts e.g. internal transistor, terminal block, headlights, ammeter, starter solenoid, GM alternator, etc.
Find more information about the Ford Tractors wiring harness and diagram in the following article (source: ntractorclub.com)