Edward,
The following is directly from the Rotax 912 heavy maintenance manual.
Trigger coil assignment (on the 912 Series)
Trigger coil A1/2 serves the top spark plug of cylinder 1 and 2
Trigger coil A3/4 serves the bottom spark plug of cylinder 3 and 4.
Trigger coil B1/2 serves the bottom spark plug of cylinder 1 and 2
Trigger coil B3/4 serves the top spark plug of cylinder 3 and 4.
Hope that is what you are looking for.
Happy flying,