It is not a factory Toyota harness. It is a curt custom wiring harness 55378. I purchased it from etrailer.com. They have a good video showing how to install on a 2001 tundra. It plugs in on the drivers side under rear bumper. I connected it as shown in video and disconnected the center wiring plug. Truck won't start, with a volt meter on the battery while connected you can watch it drain.The first photo is the wiring harness in the center of the bundle that the old 4 pin was wired to. The right side is what is still there, the left side is what I removed. The second photo is the harness that I attached the new wiring to. It fit no problem. You can see the connected pieces on the right and the now exposed connection on the left. If you follow the wiring from the exposed bit on the left it goes to a towing convertor behind the tail light. That is what is shown in the 3rd photo. Thanks!
