Tractor Repair: 1958 international 350 utility starter, line resistor, starter solenoid

Question
The original start button has been replaced by "others", with a standard key ignition switch. i.e.bat-ign-acc- and a terminal in the center which closes the circuit when key is advanced beyond spring loaded center. The starter engages, starts the tractor, but also remains on even after the tractor starts.I know that it is supposed to disengage after the tractor starts. It heats up and I suspect there is a wiring problem. The starter has been rebuilt, and I believe that the tractor has been converted to a 12 volt system. However, I don't see an obvious in line resistor, so this may not be the case.

Answer
Hello,

  To determine if it is an electrical problem, check if there is power on the small terminal of the starter solenoid after the engine starts and you release the key.  You could do this with a test light or voltmeter, or you could remove the wire from the terminal and see if the starter stops running.  If there is power at the terminal, the key switch could be sticking and not returning to the run position after releasing the key, or the switch could be defective in some other way.  Or there could be a short in the wiring or something not wired correctly.  If there is no power to the small terminal of the solenoid when you release the key, then the problem is mechanical and not electrical.  It would mean that the starter solenoid or starter drive is sticking.  The only way to know for sure if it has been converted to 12 volt, is to look at the battery.  A resistor is not always necessary.  A different coil may be installed with an internal resistor.