The plug n play ones are suppose to be plug n play and dont require it but some have problems with them not staying on and other problems so they install relays. I have plug n play hids in my fogs and I dont have relays on them, they are working good so far. The first time I turned them on, one turned off. I turn the fogs off and on again and it, or they have not turned off again since then and have been working without problems