My rear break light doesn't light up when I use my front or foot brake and I don't have a owners manual and not for sure what might be the problem. I have a 1995 883 sportster. I changed the light bulb so i know that is not the problem.

 

are ur rear breaks still working

 

Did someone change the brake lever on the handlebars or play with the hand controls on the right handlebar?
Reason: the little tit in the front brake lever (tit on switch) works opposite of what most consider normal. Out is on and in is off..The rubber tit gets broken. Button stays out which is on..most people think the brake light is broken but in reality it is ON.
Check to see if BOTH filaments are ON.
You are right the light is not the problem it is the switch...but i am guessing.
Stand in front of bike with skinny screwdriver on front brake side.
Squeeze brake lever and then with good flashlight look up into lever and press the little tit and the light will go off.

 

I agree with im, maybe your light is on all the time. I think it would be unusual for both brake switches to go at the same time - though I did have issues with each of mine at various times.

As suggested, check the front switch first.