Problem with Trailer harness on a Dodge Intrepid. No brake lights.?

I just put a 4 wire trailer harness on my Intrepid. I can either get running lights or brake lights but not both. There are two separate wires for these items one for running and one for brake and only one wire in the harness for both. Is there a way to get both running lights and brake lights with this harness? The turn signals work fine. I know all the lights work on the trailer because I had it on another vehicle to tow it.