To test amp output to coil: Disconnect the low voltage wires from the coil and connect meter to those wires. You should have a resistance of 500 to 800 ohms.

To test amp input from ECU: With the ECU disconnected, you should have a resistance of 1000 to 1500 ohms between ECU pins 24 and 25.

To test amp ground: unplug amp and check minimal resistance between brown wire and earth.