I have an EF Fairmont to which I fitted a piezo beeper to tell me when the boot light is on (as I released the boot a couple of times and forgot, thus deep discharging the battery - 3 times in a couple of months - and wanted an audible warning) and recently it's started beeping when the car is accelerating indicating that the boot light is coming on and stops when you ease off the throttle.

According to the schematic there is a relay that operates the boot lock release solenoid and the boot lamp via the momentary switch and the BCM. But I can't find that relay. Does anyone know where it is?

I'm assuming that it's just a loose contact in there that's causing the boot lamp to operate.

what you have highlighted is in the boot lock mechanism