wire/lamp identity??

That lamp tells you one of two things when it comes on. 1) the parking brake is on, or 2) there is an imbalance in brake pressures between the front and the rear systems.
-Well, if you have an auto, you practically never use that brake. And if you have a stick, its second nature to release it before moving off.
-As to its purpose as a brake failure indicator, Hah! Since it comes on after the failure has occured, it doesnt tell you much that you dont already know, as you panic brake on the remaining system.
-My bulb has been burned out for years, and Im in no hurry to replace it.
-What you do is up to you. Nice cluster BTW.