Running the 35w kit so factory wiring isn't an issue.. I think if you go 55w your pushing the oem's limit and need to use the relay kit at that point. But I'm plenty happy with my 35w. Took a little getting used to (the slight blue shade) but I like them. Might try the 5000k if and when these burn out. If I remember correctly these have a two year warranty with them also.