Trailer harness wiring

I have a 2005 Chev. Silverado 1500 crew cab with 16kmiles. When I hook up my boat trailer the turn signals and brake lights work but the running lights do not. The trailer works fine on other vehicles so that does not seem to be the problem. When I hook it up to my 03 Suburban the same problem occurs. When I hook it up to my 99 Silverado 1500 it works perfectly. The local Chevy dealer checked it and the contacts are hot for the running lights but hooked up to that trailer it does not work. Also I have a jet ski trailer and the same thing happens with all three vehicles.