you won't get the fusebox apart in the engine bay without removing the battery tray and virtually everything else around it,including the wing and the front plastic cross member so don't bother

the simplest way is to find the feed to the dipped beam and see if the earth return works

i had a problem with my lights as the return earth inside the light has overheated and wasn't giving enough whatever to get the signal to ground out so i simply added another earth wire to the loom and hey presto it worked

easiest way to do it though is to find out if there is power all the way through from the fuses to the switch to all the plugs etc