deisel glow lamp flashing

hi,

my glow lamp on my 97 alhambra tdi is flashing when i'm on the motorway , over the 60mph mark. the light wil go out when i touch the brake for about 3-4 minutes then it will come back on.
The dealer suggested it may be a brake light bulb out, but i've checked and all lights are fine.

the car appears to be running fine and it does not lack power ar anything.

does anyone have any ideas/suggestions??

thanks
steve

Go check it out at a repair garage just to be sure all is fine