Three backwoods gun nuts were busted on their way to play vigilante in New York City — while riding in a pickup truck loaded with weapons and plastered with their love of the 2nd Amendment, law enforcement sources said.

John Cramsey, 50, of rural Zionsville, Pa. — a militant anti-heroin crusader who is said to have used aggressive tactics to save at least a dozen people from drug dens — claims he was racing to Brooklyn with two pals to rescue a female drug user who they believed had been kidnapped.

The gun range owner never completed his mission. Cramsey — along with his buddy Dean Smith and the supposedly kidnapped woman’s friend, Kimberly Arendt, 29 — were stopped by cops on the New Jersey side of the Holland Tunnel for a cracked windshield around 7:40 a.m. Tuesday.

Officer John Basil noticed a loaded pistol magazine and ordered the driver, 53-year-old Smith, to get out of the truck.

Police then saw Smith had been sitting on a loaded .45-caliber handgun and later found a trove of weapons during a search: an AR-15 assault rifle, a 12-gauge shotgun and four additional semi-automatic handguns.

The cache even had a bullet clip that says “Merica.”

“The majority of these weapons were loaded,” Port Authority Superintendent Michael Fedorko said during a press conference.

Authorities also found 2,000 rounds of ammo, a bulletproof vest emblazoned with the word “Police,” tactical gear, a small amount of pot, three prescription pills and a pot pipe tucked away in the truck, sources said.

Friends of Cramsey said he has been fighting to “save kids” ever since his 20-year-old daughter, Alexandria, died tragically from a heroin overdose four months ago.

“Ever since then he has been on a mission of mercy to save kids. He’s saved at least a dozen kids by now,” his friend Jeff Feather told The Post. “He was never the same after Lexi died. He is dedicated to helping anyone addicted.”

Before he began his trip, Cramsey posted on Facebook he was heading to Brooklyn to “extract a 16 year old who up there to party.” He claimed that the girl woke up in a hotel next to a friend who had died of a heroin overdose.

“I’m bringing her out of NY today and anybody else in that hotel that wants to go home too.”

Police sources told The Post that when they found the young woman who was the subject of Cramsey’s hunt, she didn’t want help, saying, “I don’t need to be rescued.”

The girl’s dead friend was identified as Sierra, a 19-year-old who died of an apparent drug overdose Monday evening, sources said. Sources said that the girl Cramsey and his pals were looking for was not in danger and was unharmed.

After being nabbed in New Jersey, all three were arrested and slapped with several charges, including weapons possession, possession of high-capacity magazines, transport of an assault firearm and pot possession.

Authorities added that it was unclear if they owned the weapons legally in Pennsylvania but stressed they were not allowed to bring them into New Jersey or New York.

The Joint Terrorism Task Force investigated the incident and, despite the cache of weapons and gear, found no terror connections.

A Florida man who was in a holding cell with Cramsey and Smith in Jersey City told The Post on Tuesday night they said the mission was initiated by a predawn plea for help.

“He hopped in his own company truck at like 3 a.m. when he got the call last night,” said Sheldon Vargas, who talked to Cramsey. “They were trying to go rescue this girl last-minute.”

Vargas said the men claimed the weapons were only in the car for a photo shoot from the day before and they didn’t have time to unload them.

Cramsey owns an indoor gun range in Emmaus, Pa., called Higher Ground Tactical and started a group called Enough Is Enough to attempt to save kids from the dangers of drug abuse.

“He has since been on a mission to save as many of our children from the heroin dealers as possible,” his friend Susan Hirst wrote on Facebook.

“Legally or illegally, he enters heroin houses, hotels, or whatever the hell they are called. He pulls our children out of the grips of these awful scumbags!”

Earlier this month, Cramsey posted on Facebook an image that appeared to show him kicking down a door.

“Knock… Knock… Who’s There? Your Worst Nightmare Mother F–ker… AND IM COMIN IN…”

He also penned a mournful Facebook post to his daughter Tuesday, saying: “Today is the day that marks the 4 Month Anniversary of the loss of my sweet baby girl.

“Please give me the Strength of continue taking this fight to the Evil Darkness that has not just taken my Sunshine away leaving me in eternal darkness.”

Cramsey’s SUV was festooned with decals stating “2nd Amendment God Guns Guts Made America Free,” a window painted with the opening line of the Constitution, and a gas cap with a skull and crossed AR-15s.

Additional reporting by Philip Messing, Chad Rachman and Danika Fears