I’d be surprised if you have dual line brakes. You can check easily by looking at the back plate on one of the rear wheels. If it’s dual line there’s one each going to the top and bottom wheel cylinders with two brake lines coming from a similar junction on the axle.
I think Rubins is right, having looked at the manual, the brake failure warning switch does have a plug just like that. It's the sort of thing I would find on my 19 year old Fiesta though...It attaches to the brake bias valve if you have dual line brakes. The valve is located in the front drivers wing.
The wires head off to the centre console Brake check warning light.
Peter check your pm boxHi While I am on the subject of "where does this wire go" Can the top centre single and left centre double be identified please. The right one is for the alternator.
Not very clear but .......
thanks peter