How do I wire up ignition coils to an OpenECU?
The power supplying the ignition coils should come through a Normally Open (NO) relay which is controlled by the ECU's application code. During the boot sequence, the ECU enables the 5V output which causes the ignition coils to go into dwell and if the power for the ignition coil is not setup to come through a relay, then it could result in an unwanted ignition event causing the engine to backfire or rotate.
On multi cylinder engines, this will affect all coils simultaneously which will result in a high current draw on the system and could lead to a fuse to blow. By placing the ignition coil power on an ECU controlled relay, the power to the coils can be supplied after the ECU and application code have been initialized. Ensure that this is not the same relay through which the ECU also gets power from. Most vehicles refer to this relay that powers the ignition coils as "powertrain" relay.