GM-GMC: trailer wireing, trailer wireing, trailer package

Question
I have an 04 GMC half ton with the trailer package, when i hook up my new small snowmobile trailer all the lights will come on but when i hit the brakes they all shut off. any ideas? Thanks

Answer
I am wondering if other trailers do the same on your truck.  If not, it sounds to me like a ground problem on the trailer.  If the trailer is new, I would definately be contacting the retailer and asking them to look into it or replace it.  If you are stuck with it, try unhooking one light and trying it, try to narrow down where the problem may be.  Check the routing of the harness, I have seen many harness' with screws put right through them from the factory, and it causes stupid stuff to happen, not unlike what you described to me.  I am doubting it is your truck that is the problem however, keep in mind though, the 7 way connectors have been known to get contaminated and corrode.
hope this helps