The coil... Does this refer to the spark coil? It is risky to give it a direct connection to low voltage circuitry.
Instead consider placing a sensor near a spark plug wire. It might be a simple coil of wire.
Or, I once wrapped a bit of aluminum foil around the main spark wire, then jumper-clipped it to my oscilloscope. I triggered the sweep off #1 cylinder. Then I could watch the intensity of spark to all cylinders, one after the other.
Be careful not to squeeze spark plug wires. High voltage can penetrate the insulation. That is why your sensor should not touch the wires, but be located at a small distance.