I bought an adapter for my cherokee to use the trailer lights and keep blowing the parking lamp fuse. It is wired as the instructions say. Before i used the adapter, it did the same thing. The wires are all new and properly insulated. I put a 5 amp higher fuse just to see and blew it in a few minutes. If I remove the trailer wiring, the fuse doesn't blow

Find & repair the short to ground. Don't re-engineer the electrical circuits with out having a fire extinguisher nearby.

Could be a short in the trailer wiring?

I tried 2 different harnesses. I must have done something wrong, but all the cables look fine. I will have to tear into it again tonight

When you say you remove the trailer wiring do you mean un plugging the trailer or removing the harness from the jeep?Is the fuse blowing when you have the trailer unpluged?