Going from memory, COULD be wrong.....
Have GW 26DBH, 2014 model. Probably same setup....
It took my pea brain a while to figure it out, but A, B, and C are confusing. To figure it out, I had to turn all off, then turn A on and off till I figured out where it was coming from. Then turn ONLY B on till I figured that out. There is no way to have 2 or 3 of them on at same time that I can figure out.
If I am not mistaken, A is inside, B is outside, and C is useless. HOWEVER, I have not once tried the DVD player (we're old and "tunes" ain't a biggie to us!!
) So, it could be for that alone..........
I realize this isn't much help, sorry.