There should be a matching white wire on the light harness coming from the truck. Make sure that this wire is attached to a good ground source somewhere on the truck frame. Boot's suggestion to use jumper cables is a good one - it will tell you right away if you are not establishing a good ground between the truck and the trailer. It's all pretty simple, really - the ground side on your trailer lights have to find their way back to the negative side of your truck's battery somehow. That's why the lights work when you hook them up straight to the battery.

Thanks guys for your help. Apparently it was the truck. We got another truck over here and lights worked fine. Now we will have to figure out what is wrong with the truck, but after this weekend. Thanks.