Does the fuse look good, or have you changed it? Even if the fuse looks good, I would change it because it may not be good due to hairline cracks or corrosion.
Next I would check out the brake light switch. It is mounted on the steering column tube, I think, directly above the brake pedal. On my 4.5 the switch started sticking and the brake lights were delayed in coming on for a few seconds. Replacing the switch cured that problem. Could be that your switch has stuck completely. Check it out.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.