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If you don't have adequate resistance you will fry your switch (electronic points) and it will stay shorted (like points staying closed all the time) which makes your coil get very hot and obviously it won't fire the plugs.

I know because the other day I was troubleshooting a neighbor's tractor. His had a coil with an internal resistor and hence the tractor didn't have one. I took the coil and trigger mechanism from another tractor and installed it. It lasted about 2 minutes.

Trouble shooting later, I found that I had put in a 1.7 ohm coil and not having an external resistor to make a total of 3.5 ohms, I fried the electronic points.

$100 down the drain trying to help a neighbor. Oh well.

Mark

With that rig, you can run the red wire to the + terminal on the coil which is getting 12v via the ignition switch and the black wire goes to the coil - terminal.

Otherwise, if you have a ballast resistor, you have to add some wire to the red lead (insulated connections and wiring) to get on the battery side of the ballast resistor to get the 12v required.

Not getting 12v won't kill it. It just may not run properly. Not having adequate circuit resistance WILL kill it... BTDT.

Mark

HTH

Mark