I'm trying to replace my halogen bulbs on my '18 with LED's (I bought Sylvania ZEVO 921 bulbs). I saw a posting on the regular Cadillac Forum where a guy replaced his halogens and found that the LED's "stay on a dim setting and will not totally go out" or only one bulb will work. He says that the circuit doesn't have enough resistance to work with LED's. He claims that you need to add an in-line resistor to get them to work right. I have the carbon fiber package and getting to the bulbs is going to be difficult so I don't want to go through the effort if the bulbs won't work.