When i hook my trailor's lights to my 2003 yukon xl, park lights doesnt work, but all other lights work

You mean the truck parking lights dont work, or the trailer running lights dont work? Does the trailer just have tail lights or does it have front and rear side markers? I think you mean the trailer lights. Check for power at the plug,(Brown Wire) if there is power, then you could have wiring problems, but a better description of what works and what doesnt work needs defining.