The lights work on my trailer for turn signals, brakes, and hazards but the lights don't come on when I turn the headlights on in my truck.  They do, however, work when the trailer is hooked up to another vehicle.  Obviously there seems to be a problem with my truck.  I tried a new 7/4 converter but it didn't help.  Does anyone have any suggestions?

i had a similar problem..i ended up changing the taillight converter(i think thats what it's called) it's a small box underneath the truck that your truck wiring goes into and then comes out the other side to the trailer lites...i have a 2003 nissan and the old one just unplugged from thr truck wiring and i plugged the new one in and presto!..everything worked..i spent a week checking wires and bulbs......

Are you talking about the converter or the hub?  I've tried a new converter but didn't have any luck.  I'm thinking maybe there's a blown fuse.

it was the converter,i don't know what a hub is.....it seems that your lites wouldn't work at all if a fuse was blown....on mine i checked the dc voltage and when i turned the headlites on it would drop way down,so i assume there was a bad wire in the converter.....but it was doing the same thing as yours..turned the headlites on and got nothing...i guess you should go back and check grounds,i'm guessing that when you turn the headlites on the voltage is drawing off somewhere else not giving your lites enough power to lite up....something in the headlite circuit...

do they work when the headlights are off? If so it sound like a ground issue. make sure your wire is hooked to a good ground under your truck.

Are you talking about the converter or the hub? I've tried a new converter but didn't have any luck. I'm thinking maybe there's a blown fuse.

Depending on the make and model of your truck, there may be seperate fuse under the hood that sends DC to you trailer lights.