The ECU has 2 outputs for ignition. One for cylinders 1 & 2 and one for 3 & 4 as it runs a wasted spark system i.e 1 and 2 fire at the same time but only 1 ignites due to the other being at the wrong end of the stroke.
I also expect that the ECU switches the negative side of the coil.
It may be a live feed to the coil, a ground to the coil and the 2 signals which go back to the ECU. Buzz the other signals at the coil, if one is connected to earth then pretty sure the other 2 are the ECU outputs.
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