No need to post the photo, from your description your first statement and VinceU were correct the black with the B goes on the ground post.
Now you need to deal with those hot light bulbs. Yes I switched to LED bulbs recently got 30 of them on EBay for $25 including shipping. The ones I got may not be bright enough for you since you stated you had all 3 lights on in your TT at once, I prefer lower light so I got the ones that are kind of bluish in color and not real bright. I don't know from experience but people say the bright white ones are closer to regular bulbs in brightness.
You can use the search I mentioned earlier to look more into LED's if you scroll to the top of this page you will see the search tool in the large green area, type LED lights in the white space, just below the white space you choose between FRF or Google you don't want Google choose FRF (Forest River Forum) and you will get a listing of forum discussions on the topic.
Dale & Terri, Lulu & Tiki (our Chihuahua's), New rescue puppy Prince - Pom/Pug mix.
2013 Tundra, Double Cab, 5.7, TRD Off-Road, 4X4, Full Tow Package
2013 Wildwood T26TBSS - Sold
2000 Gulf Stream Sun Voyager M-8357 MH, Ford Trident V10 Gasser, 35 foot.