One of my number plate lights failed. Not a big job so I coughed up for a pair of LEDs. Hauled out the blown bulb and found out why it wasn’t working. Corrosion had set in and the little wires that lead from the capless bub had cracked. Put in the first LED. Didn’t work. Tried the good bulb from the other side. More corrosion and it also broke when being extracted. I tried scraping off the rust. Still no joy so a brainwave followed. I stuck two strips of aluminium foil down into the socket to increase the chances of a few electrons getting to their destination. Success! Not as bright as the other one mind.