Why wont the headlights won't go on

Check your head light bulbs, your truck has the dual filiment headlight bulbs one per side which does both high beam and low beam, 9007 bulbs.
If the low beam filiments are burned out only the high beam will work.
Also look into finding out if the headlight switch is gone bad.
The headlight module and or drl module maybe defective.

Chech the head light switch the point of contact could be rusty and the head light relay

Pulling back on the dimmer switch is using the "flash to pass" feature common on most cars and trucks. You are putting power to the high beam circuit without using the headlight switch.
You would need to check for power in and out of the headlight switch for the headlight circuit, and then the dimmer switch. On models built after 1996 the headlight switch grounds the lights.

Headlight switch is worn out, had the same thing on an old Ford pickup truck.

Are sure the dash dimmer control isn't turned off at the headlight switch?

Replace switch.

SOUND LIKE FAULTY DRL HEAD LIGHT RELAY.CHECK HEAD LIGHT RELAYS YOU HAVE RELAY STAYING CLOSE NOT OPEN TO TURN OFF CONTROL CIRCUIT TO HEAD LIGHTS.

your switch is bad. had same problem on my 1970 mustang with the headlights flickering unless I pulled on the switch. I replaced the switch and they work fine now.

THE SOLUTION WAS THE HEADLIGHT SWITCH. IT TURNS OUT THIS IS A COMMON PROBLEM ON THIS PARTICULAR MODEL. THE BROWN WIRE USUALLY BURNS UP. CHECK ALL WIRES AND CONTACTS BEHIND HEADLIGHT SWITCH. TO PULL SWITCH, THERE IS A RELEASE BUTTON ON THE BACK SIDE OF THE SWITCH. PRESS THAT BUTTON AND IT WILL REALES THE PLUNGER. PULL THE PLUNGER ALL THE WAY OUT AND YOU WILL BE ABLE TO PULL THE HEADLIGHT SWICH OUT. i JUST REPAIRED BROWN WIRE AND CLEANED CONTACT. VOILA.. RUNNING LIGHTS ARE NOW ON. THAT RELEASE BUTTON ON THE SWITCH IS A BOOG TO GET TO THO. GOOD LUCK

check your head light switch