that's what I was thinking too! maybe it's just a bad connection but I can't see how to get into the unit! The Antara is going into the garage so I'll ask them to have a look at it and see what they say!
Hello Micknut and welcome to the Antara forum. Don't think the OP ever came back and said what the final outcome was. The high level brake light is fixed into the rear spoiler, to remove it you need to open the tail gate and remove the four nuts at the top (see pic for the L/H pair). Once you get all the nuts off there's four studs left which are screwed into the spoiler. You have to semi-close the tailgate then work the spoiler free and lift it off.
Although the brake light is ok on my Antara,i had a similar problem on my previous Insignia.
I took it out pretty much the same way as described here and it turned out to be the multi plug not quite seating in.I pushed it in,it clicked then worked from then on.It actually may not have been seated right from new and the action of closing the tailgate (on the Insignia the tailgate weighs twice as much as the Antara) caused it to loosen off.Hopefully yours will be just this but they are reasonable price on Ebay.
Top level brake light is out on mine but most of the nuts are just rotating so can't get spoiler of. Considering using a nut splitter on the whirling ones then hopefully can glue the bits together once i get spoiler of and fit new nuts. However they are domed and not sure if splitter will work?