Light blinking means hatch or door switches aren’t working - engine bay alarm pin switch should be disconnected for this test too since hood is raised.
Measure the current draw even with light blinking. You’ll see it swing from around 50mA to about 200mA due to light bulb draw when glowing. If you get say 500 to 700mA or more with the security light blinking the alty is likely bad due to failed diode bridge.