Hi Taimur and welcome. Have a look on the "introduce yourself" thread where you'll find a useful template to tell us a bit about you and your truck. We like to get to know people a bit and love seeing photos once the magic 15 posts has been reached.
On the rear brake light, I can't add much to what I posted on the other thread you found. Once you get some photos up it may be more apparent.
Stupid question, but if you have an owners manual does it not say in there how to remove the cover to change bulbs etc?