hi i have a 01 expedition and i changed my factory headlight to the euro lights,so my driverside light went out and changed it(H1 bulb) but when i changed it, it still did not work so i turned on the brights and the brights work,so i went and put the factory unit back in and the same thing the brights only worked does anyone have any hints that can help here what is weird is it is only the driverside,well thanks

 

It has to be wire or socket problem.
Power is common to both sides.
Socket may have been over heated by the non stock lamps and tension lost.

 

That is exactly what happened to mine. Check the socket!