My brother has a 04 dodge ram 2500 4x4. Im trying to help him fix it but not getting any where. The problem were having is when you turn the headlights on the brake lights will not work. Now if you turn the headlights off the brake lights work. Can anyone tell me whats going on? I made sure all the bulbs in the taillight socket parts there all good. Does anyone know what size bulbs should be in the taillight part? The is a ground on the passenger side on the box and hooks to the cab i cleaned that up and still no difference. Is this a ground problem if so where else are there grounds at? I also checked all the fuses and they are all good. If anyone has any idea that would be great. Thanks for any info thats given!!!

 

I believe 3157. They are a blade style. Check the tail light circuit boards. Could be your issue

 

Thanks for the reply. Here is what i done i went and got brand new circuit boards for both tail lights and brand new bulbs and still nothing. I was checking the wires and somehow i must have touched couple of them together and now there is no lights coming on in the taillight on the driver side. I checked all the fuses and ever fuse is good.