I recently got a 1984 Ford F-150 i6 300 2wd 4 speed. Got rust and dents but that's all going to be fixed. That's not the point. My blinkers work, both front and back, by brake lights work, but not running tail lights and running headlights. I replaced both my headlight switch and the floor dimmer switch and it did nothing. Lights work good when hooked straight to a battery so why are they not working now?

 

Could be a loose connection or contacts.

 

What about the relay, have you inspected it yet?