In the trunk is the radio receiver, mounted on one side of a piece of sheet metal. On the other side of the same piece of sheet metal is a black box that looks like an amplifier with cooling fins.

I don't think it is associated with the sound system. Anyone know what it is please?

There is 12V on a black control wire coming out of the radio receiver to provide 12V to the power antenna on a blue wire. The 12V never reaches the blue wire.

Does anyone know where in the car to find the connector between the black and blue wire please?