Just to confirm it is definitely a 501 capless
I bet replacing the bulb wont work.... 
he says he hasent got one in there atm thats why he is replacing it...
common problem for the boot to get wet from the washer jet and feck up the boot switch and other electronics.
The micro switch in the catch can fail, which does prevent the bulb from illuminating, it also stops the 'luggage compartment open' warning from appearing on the dash.
