Just purchased a 2003 F250 with 7.3L Diesel and have been trying to fix some of the quirky things that are going on with it but I am stuck and hoping someone could help me out. My regular headlights will not work, only high beams work, they work when they are on permanent or when I flick the high beams. The bulbs are in working order so I have eliminated that as the cause of my problem. The headlights have a 3 wire connector however the bulbs are different since the previous owner put newer style headlights on the truck.
I have hooked a test light up to the Neg battery terminal and stuck the other end into the plug where I believe the high beam connection is and when I turn on the high beam the test light comes on. I did the same thing with the Low beam part of the plug and cant get the test light to come on,

My next step was to take the test light and connect it to the positive battery terminal, stick the other end into the ground wire part of the connector and the test light came on

here is where I run into my problem, when I connect the test light to the positive terminal on the battery and then stick the other end into the low beam part of the connector my test light comes on, I am assuming that somehow the wire is grounded out somewhere but would like any other suggestions that you could give me. I am also wondering if that wire is grounded out wouldnt that blow a fuse? all of my fuses are in good condition so that is not my problem. any help would be greatly appreciated.