I replaced the ignition switch on my D2350. I don't recall it having a color code. There were small letters by the terminals. One wire coming in is always hot. Use your voltmeter to find it. You can then touch it to each of the other wires to see what happens - glow plugs, starter, etc. You can use your ohmmeter to identify what terminals on your switch connect for the different positions. If using an automotive type ignition switch to replace the tractor switch do NOT use the ACC position for the glow plugs!! It is hot whenever the switch is on.