wiring for EFI

The reason you must tie them together, is that during cranking, one supplies 12v directly to the coil, and the other is dead. Then when you release the key to run, the "direct to coil" 12v goes dead, and the other gets 12v, which routes through the ballast, reducing voltage, and then to the coil. Together they will ensure you have a full 12v to the coil (or EFI ECU) during cranking and running