Have Mustang 2016. Had to replace my 35w HID for 25w (legal reasons) and now headlight wont turn off until I disconnect battery or pull fuses. All parts are made by Osram and Plug'n'Play. Normally you would say "Check relay" or "Check fuses" and this is where it gets bizarre- I switch 35w parts back on and everything works fine. Connected car to Forscan, no fault codes. What can be different that 25w parts don't like, but for 35w parts it is fine. Logically there can't be.