TD5 Flickering handbrake light

Hi, I've searched the forum and taken as much of the advice as I can - stripped down handbrake switch, split connector (under central seat panel) and cleaned (it was quite badly oxidised), checked connectors on brake fluid reservoir. When i first cleaned the central connector it seemed to work, now it comes on flickers and dies - to try and elimanate the switch, if i connect the central connection wire to earth, it does the same - dash light comes on flickers and dies and then won't come back on (maybe the odd little flicker as i move the connector on the earth.
Strangely it only comes on (briefly) when the engine is turned on - not just with the ignition turned on?
Maybe the bulb? Suggestions greatly appreciated - it's not a big deal but niggles a bit...
Cheers

if it bothers you change the reservior cap

THANK YOU!!!!!! Been going potty checking the handbrake circuit as above - completely forgot I doh!) that its a fluid level check too......! I know the fluid level is fine - I do check these things - so the sender/cap seems an obvious target. Isn't it daft getting sidetracked up a blind alley (is that too many metaphors mixed.......?) - step back and think sometimes! Much appreciated. Cheers, A