Test the ground of coil by clipping one end of your tester to the positive terminal of the car battery and the other end of tester to the ground wire of the coil. 1 IGT (Ignition Trigger) Signal from the ECU that commands the coil to fire (low-voltage pulse). 2 IGF (Ignition Feedback) Return signal to the ECU confirming that the coil has fired. 3 B (Power / 12 V) Ignition power supply — usually from the EFI or IGN fuse. 4 Ground (E) Ground connection — usually to engine or ECU ground. #car #auto