The LED alarm light LED is at 0 volts when it's off, and 1.5 V when it's in alarm state.The LED (+)(-) lead can only be used to connect to the MOSFET Source and Gate pins if the (-) and (+) are at zero volts vs. ground when the LED is off. I don't think this will be true. I suspect that they will be at
12 to 13 for (+) and something random between 0.5 and 10.5 when off and
12 to 13 for (+) when and 10.5 to 11.5 when on
Remember, measure from chassis ground to the pin in the DC voltage mode and report values.
The Strip LED (12V) has 12VDC on the (+) lead at all times.