I have a 2013 F150 Fx4 . I installed 3157 switchbacks ,bulbs light up white if slightly inserted into socket but no blinker/ flasher. I can remove bulbs rotate 180 degrees re-insert into socket and they light up Amber while flashing but no other function.
Thanks guys. I found that experiencing residual voltage from the turn signal module not allowing the running lights(white lights ) to come on . Load resistors solved that problem. I still haven't found out how to perform the bambi mod.