You will need to pickup the running light with a new wire. If this is on your BMW the rear will be easy to pick up from the tail/running light. The resistor would wire parallel to the load (one lead from the resistor to ground and the other to the + or hot to the bulb. A 50-watt resistor would be huge so its possibly a 50-Ohm x 5-watt but not sure where the value you stated come from. What is the reason for the change to the LED's? Just curious as I may want to do the same on my RT lol.
Always aim where you want it to go and never at people (DakarNick)