Onan no spark while cranking but fires when key is

If it does, in fact have breaker points, here's what you need to check.

1.) Check your battery voltage WHILE CRANKING with the starter. It should be above 9 Volts, if it's below try a known good battery.

2.) Take a close look at points to see if they are discolored and burned. If the switch was left on, this is likely.

3.) Likely, the coil has been damaged by the internal heat generated by the battery draining through the coil when the switch was left on. You will probably need to replace the coil.

I think that Ron in AR is on to something. I don't know about your Onan engine, but commonly, there will be a resistor in the primary coil circuit. If that resistor exists, there is usually a wire from the "Start" connector on the ignition switch or from a small connector on the starter solenoid etc., that provides the full battery voltage to the coil during starting (bypassing the resistor) but then goes away when the ignition switch is released to the "On" position. With the switch in the "On" position, the battery voltage is applied to the resistor which reduces the voltage that is subsequently applied across the coil.

So, if battery voltage is not getting to the coil when the ignition switch is in the "Start" position, the engine won't have any spark while cranking, but when the ignition switch is released to the "On" position, it will have spark and might start.

You might want to ascertain whether or not you have an external resistor, and then how that resistor is bypassed during starting. I think you might have a problem in that bypass.

Good luck,

Tom in TN