I have a factory towing package setup on my 2007 Tacoma. It has a round 6 or 7 flat pin plug (can't remember 6 vs 7 at the moment). I sometimes borrow a friend's trailer that uses a 4-pin plug. I bought an adapter and it works great during the day. The signals and brakes work fine. But once I turn on the truck headlights, the trailer lights will come on and no longer work with the brakes and signals. The trailer lights are on, but it's like I'm driving around with the trailer brake lights on 100% of the time as long as the truck headlights are turned on.