Headlights/taillights on 1994 f-150

I have a 1994 f-150. I’m having trouble out of the
headlights/tail lights. I put a new switch and pigtail
harness in it. (All wires are correctly matched up to where
factory wires are) But when my head lights are on, my tail
lights do not work. When I have my headlights off, my tail
lights do work. What could be the problem. I replaced the
switch and the pigtail. And I checked ever fuse on the
truck. None of them are bad