Back running lights won't work, blinkers and brakes both work changed the fuse and light bulbs any suggestions why the tail running lights won't run

Would need to test power from the headlamp switch . Go to http://www.bbbind.com/free_tsb.html free wiring diagrams. Enter your vehicle info , year ,make , model an engine . Under system click on lighting ,then under subsystem click on external lights .Then trace out where the tail lamps get power , do you know about automotive electrical circuits ,how to read a wiring diagram . Go on youtube check out videos on basic automotive electrical trouble shooting , how to do voltage drop testing an how to read wiring diagrams . Then get yourself a DVOM - digital volt ohm meter . Then test the circuit ! That's how automotive electrical problems are found .