I have a 2006 F150 4.6, the brake display on my dash comes on intermittently,sometimes for weeks, I've changed the emergency brake light switch, the brake light switch, the master cylinder and checked all the calipers over the past 2 years and it is still on, what can this be???

 

Have you checked the switch in the master cylinder?

 

Could be the cluster itself.

 

Is the fluid reservoir at least half full?

 

Had the same issue, my problem was with the cluster. I re soldered the surface mount resistors and the connectors on the cluster and it solved the issue. Search for cluster repair there is a thread. If you don't feel confident in doing this yourself there are places you can send the cluster in for repairs.