Ohm's law is your friend.
Keep in mind in a 5W5 bulb there is a current flow of 0,42A at 14V.
So you've to add a parallel resistor to your LED that dissipates the difference between the current of the LED and 0,42A.
Mind the wattage: a 56 Ohm resistor at 14V dissipates (14*14/56) 3,5W, so you'd have to choice at least a 5W resistor.
For example: if in your LED there is a current of 0,2A you've to add a standard 68Ohm resistor.
Every resistor that dissipates current becomes warm/hot