The Function of the Auxiliary 12-Volt Connection on the 7-Way Trailer Connection

Question

Question:

What is the function of the 12 volt battery in this type of trailer? Can the interior light be turned on with the trailer NOT connected to the tow vehicle?

asked by: Russ F

0

Expert Reply:

The auxiliary 12-volt wire that runs from the 7-way connection to 7-way trailer plug will supply 12-volt power from the vehicle to the trailer. The 12 -volt power will allow interior or exterior lights to run that are not wired in to the trailer's tail and clearance lights. The light will operate separate from the trailer clearance and tail lights and will not need to have the truck light turned on to work. The auxiliary wire will also allow you to use other 12-volt trailer accessories, like an electric jack. This auxiliary 12-volt can also supply a maintenance charge to the trailer's battery and breakaway battery.

If you have a 4-way flat plug, then your interior trailer lights must work only when you have your tow vehicle's lights on and connected to the trailer.

Unless you have a separate 12-volt battery connected to your trailer, the interior trailer lights will not work if not connected to the tow vehicle.

Also, keep in mind that leaving the electrical connected between your vehicle and trailer over a period of time can cause your vehicle's battery to drain.

expert reply by: Jared P

0

Michael

3/12/2024

Where can you find the connection to the auxiliary lineunder the trailer

Reply

Jesse M.

3/13/2024

@Michael No way to give a specific location I'm afraid. Even if we knew exactly what trailer you have there is no way to look this up. Your best bet would be to simply trace that wire back from the trailer 7-way. Just start at the tongue and work your way back. If it were me, I would start by checking the driver side frame rail.

Reply

Sid 0.

4/9/2024

When is the Aux power supply hot ? Only when the ignition is on ? -OR- Hot all the time like a cigarette lighter socket ? Thanks Sid.

Reply

Justin

9/11/2025

@Sid0 depends on vehicle, typically in my experience trucks from 2000 and up it is switched with the key if using OEM trailer wiring. SUV's depends on manufacture on how they set up their OEM trailer wiring system, and finally if the wiring was added to any vehicle that did not have OEM wiring for trailer electrical functions it is anyone's guess and will need diagnostics performed.

Reply

Answer 1

Some trailers may need an auxiliary power source to power additional 12 volt items on the trailer but this isn't as common as you might think. Now instead of aux power reverse lights are more common on vehicle side trailer connectors (and still…

view full answer...

Answer 2

The only pin that should be continuously showing 12V power on the 7-Way connector on your vehicle is the 12V power circuit which is normally the black wire but not always. In 7-way wiring the 12V auxiliary power feed is carried on the contact at the…

view full answer...

Answer 3

If you will be towing a trailer with LED lights then you will likely need to use an adapter with a lamp-out sensor like the Tow Ready #20142 or Curt #C57003 that you referenced. Both of these adapters will accomplish the same task; plugging into an…

view full answer...

Answer 4

You would not be able to charge your battery through the wiring on your 4-way trailer connector. Since your truck has a 7-way connector, you could maintain the power to the battery but not charge it. To begin, you would need to cut off your 4-way…

view full answer...

Answer 5

If you check out the picture I attached the middle set of 7-ways is the wiring diagram/colors you'll need to use for the Ford Replacement OEM Tow Package Wiring Harness #118243 that you referenced. The harness is already wired up correctly though…

view full answer...

Answer 6

It sounds like you're asking about the 12V circuit on the 7-way trailer connector on the rear of your 2003 Chevrolet Trailblazer. Some vehicles will always have power and some others will not. We don't have this specific information for your…

view full answer...

Answer 7

Most if not all trailer wiring harnesses/connectors use larger wires for the 12 volt and ground circuits compared to the other circuits (lights). The sockets themselves don't have an amperage rating so you will go by the draw of the things…

view full answer...

Answer 8

When wiring a trailer connector, it is best to wire by function, as wire colors can vary. We have an excellent wiring diagram on our website, I will provide you a link so you can look at it. If you are looking at the inside of the trailer connector…

view full answer...

Answer 9

The Bright Way Trailer Brakeaway Kit #3802308 has a built in 1-AMP charger. So when your truck is connected it will be charging. There should be no draw going out while the trailer is disconnected so it should be ready to rip whenever you're…

view full answer...

Answer 10

The ring terminal size you need for the posts of the junction box part #3375601101 that you referenced is 3/16 inch like the part #44-5310A which would work great. The terminal matches the correct ring size and also is designed for 10 to 12 gauge…

view full answer...

Answer 11

The Buyers Products Trailer Wiring Junction Box #3375601101 referenced in your question measures 6.5 inches long, 3.21 inches wide, and 2.5 inches tall when the cover is installed. The mounting holes at each end are spaced apart 7.38 inches on…

view full answer...

Answer 12

In order to find a replacement king pin that will fit your trailer, you will need to determine the model number for your existing pin box. Since you are unable to read the number stamped onto the unit itself, you still have a couple of options.…

view full answer...

The Function of the Auxiliary 12-Volt Connection on the 7-Way Trailer Connection

Product Page this Question was Asked From

Continue Researching