Did Faulty Trailer Wiring Burn This FJ Cruiser To The Ground– Twice?

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Patrick of Dallas, TX had been towing with his 2012 Toyota FJ Cruiser for months, until a run with a rental trailer turned his truck into a ball of fire. Can we figure out what happened?

Patrick took to FJCruiserForums to share his plight, video and a few pictures as well as a detailed account of the incident and some advice to other owners hoping to hook up trailer wiring to an FJ. But most importantly, he described his hypothesis as to why his off-roader was consumed by fire and reduced to rubble.

Yes, it's in portrait mode. Let's move on.

Basically, he'd had his trailer wiring installed by a professional and the truck had been towing his camper for a couple incident-free years. The camper used a seven-pin connector. On the day he pulled a rented utility trailer from Home Depot, requiring him to hook up his four-pin connector for the first time, he was flagged down by another motorist who was alarmed to observe the FJ was billowing smoke.

Patrick had been towing the trailer for inside twenty minutes.

He called 911 and the fire department was dispatched quickly, undoubtedly using some of the car-fire extinguishing techniques we've discussed before. The fire was put out, the Dallas Fire Department satisfied with the scene's safety, and a tow truck was sent to pick up the scorched FJ.

But by the time the wrecker could arrive on scene, about an hour later, smoke appeared again... and soon 4X4 was completely engulfed in flames and obliterated. DFD returned to finish the job, assuredly with a little embarrassment.

Patrick has some ideas about what might have happened, but he admits his assessment is speculative and declines to specify the wiring installer "in case he's wrong," which is a classy move. What the hell do you think happened here?

In his own words:

Link:
Did Faulty Trailer Wiring Burn This FJ Cruiser To The Ground-- Twice?