hooking up trailer lights for 93 chevy astro van

I have not been able to figure out how to hook up my trailer lights for my 93 chevy astro van. I took the van to a mechanic and he says that he cannot figure it out either, he tried to hook them up and when I got home they did not work. So, I bought a plug in tester for the hook up and it did not work. I have tried the tester on another vehicle and the tester worked on that vehicle. So, I know that the tester is good. I would like to know where I could get some sort of diagram that would show me how to hook up the trailer lights, and I dont know where to find one at. Could somebody please help me with this problem??