Trailer plugged to tow vehicle

[Norm excella]

Without a battery hooked up in my airstream, what should I expect to have power from my truck when the 7 way plug is connected?


Norm

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[Rich W]

Since there is no battery in the box, I would expect that nothing in the trailer would have 12vdc power.

[ALANSD]

running lights

[HowieE]

The exterior light are powered from the truck and have nothing to do with the trailer battery.

You should have all 12 volt functions in the trailer because the 12 volt feed from the truck goes to the common positive terminal in the distribution panel. That said do not attempt to turn on much more than one light at a time as the wire coming from the truck is too small to support a heavy current draw.

[Chuck]

...and it depends on the truck, too.
On my Dodge, the +12v charge line is always hot, whether the truck is running or off. This feeds the 12v circuits in the trailer, so everything should work.
I've done this purposefully to get a "boost" toward the end of a boondocking outing, when the trailer battery is getting weak, lights are dim....plug in to the truck, and "poof"--lights brighten up.
Just know, you're draining your tow vehicles battery when you do this.

Other makes/models don't leave the +12v hot, unless the vehicle is running.

[Bk Yd Safari]

sorta related??? if I have a dead battery on the tv and fully charged batteries on the trailer can I plug the trailer into the tv and jump start the tv?

[DKB_SATX]

Originally Posted by Bk Yd Safari

sorta related??? if I have a dead battery on the tv and fully charged batteries on the trailer can I plug the trailer into the tv and jump start the tv?

You might get a little assistance for a weak battery that can barely turn the truck over, but if the truck battery is really dead, the charge line through the umbilical wouldn't have the capacity to help start the truck even if there's not an inline diode that prevents backfeeding to the truck.

You'd do better removing a battery from the trailer and hooking up to the truck with jumper cables.

[Rich W]

Trailer breakaway brakes won't work if there's no charged battery connected; right? That would be a little dangerous.

I knew the exterior trailer lights would work, I thought he was asking about the interior 12v usage. To tell the truth, I'm surprised that anything would work on the inside with no battery in the circuit. I learned something today.