Wasnt sure were to post this so i figured this is my weekend driver/ tow rig.. this forum might help. I have a 01 Dodge 2500. Dad had it last weekend and he said he changed out a headlight bulb that had gone out. Now the fog lights wont turn on when the headlights are on.. They come on when the running lights are on but when then the next switch to the headlights kills the fogs! Checked numerous fuses in the dash and under the hood. Any suggestions? Thanks

first off, check the bulb he put in to verify it's the correct part number.

are you sure that the high beams aren't on by accident or something is wrong with the dimmer switch to keep them on?

Fog lights should not work when the high beam headlights are on which leads me to believe either the wrong bulb is installed which is backfeeding the high beam circuit thus killing the the fog lights.

A dimmer switch malfunction is possible but awful strange this started as soon as the bulb was changed.

thanks for your help, just purchased new headlights all together. (wanted black ones) So when i get to it im going to check all the bulbs and make sure they're matching. Appreciate the help. Thanks.