I recently bought a Focus Mk2 1.8TDCi Ghia 07 plate and decided to fit a hands free kit. When fitting I noticed that on the panel under the radio there are 4 slots from left to right as follows;

Blank - Headed windscreen - Heated rear window - Blank

The far left blank has a connection to it but it is blank, does anyone know what the wires are for or if they even do anything? Would buying a button for it make it function?

Any info would be great, thanks