You did not give me much to work with, but I have a sneaking suspicion I can figure this out. Your ignition switch uses two totally different parts to send current to the ignition coil. One part turns on only in the "crank" position, and the other part only turns on in the "run" position.
What I would do is unplug the red/blue wire at the starter solenoid near the battery so you can do some testing without the inconvenience of starting the engine. Now go to the ignition switch and look for the two yellow wires. Back-probe them and verify they both have twelve volts.
Next, hold the switch in the "crank" position, then check for voltage on the brown/pink wire. If that is there, my guess is your symptom is the engine will run as long as you hold the switch in the "crank" position, but it stalls as soon as you release it to the "run" position. To verify that, leave the switch in the "run" position, then check for twelve volts on the red/light green wire. If it is missing there, replace the switch. As further proof of my great wisdom, you will have twelve volts there with the switch in the "crank" position.
Also, examine the terminals on the switch and in the connector. If one or two look black, or the connector body is melted, I will describe how to handle that. If you just plug in a new switch, it might solve the problem for now, but the same thing will happen again in short order.
Saturday, May 20th, 2017 AT 10:04 PM