Jesus, this thread is full of mixed and often off information.
The BLACK/WHITE wire is the positive feed from the fuse block. The same wire has a splice and feeds both coils.
The BLUE and BLUE/WHITE are the computer-controlled ground sides.
If you are jumpering the black/white wires, you are simply adding another splice. The black/white wires are already connected.
If you want both intake and exhaust side plugs to fire, you would need to jumper the blue and blue/white wires together.
This information applies to all model years of CA20E and CA18ET per all the FSM manuals that I have.
The S12 does NOT have a waste-spark system, and the dual-coil mod does NOT convert the system to waste spark. When you jumper the system, it is like running two entirely independent spark systems simultaneously. There is no waste-spark action.
If you disconnect the coil and transistor assembly completely, you can measure the voltage present at the connector. You will find with the key in the 'ON' position there will be 12V at the black/white wire's terminal. Feel free to check this before you do this mod.
If you jumper the blue and blue/white wires, I would do it before the transistors.
I personally don't care too much for this mod, I don't think its particularly necessary or a good idea, but if you want to do it, do so at your own discretion. Several people have done it without issues.
Once I have some time, I'll put together some pics and diagrams, unsticky this thread, and put the info in a new one and sticky that, to clear up the confusion. I will also add all the technical reasoning and logic behind these statements.
Please refrain from discussing the V6 motor in this thread, seeing as its aimed at the cursed 8 plugged 4cyl cars