So I ended up having to get one of those adapters that plug between the tail light harness for trailer lights. Now when my lights are on or I hit the brakes the rear turn signals on my truck don't work. The front and trailer lights flash fast like my bulb is out. When I don't have lights on or braking then they work.

What's going on?

 

It sounds like you've lost chassis ground for the rear lamps. Double check the adapter, ensuring its properly connected/correct application for your truck. If you're still having problems remove the adapter and recheck the lamp operation. If they work, try a different adapter.