Quick-Connect Trailer-Wiring Harness
7-Way Adapter Plastic

List price:
$24.95

$22.50 $22.50 $22.50

Delivery Options

Order by 1pm for delivery today. Orders after 1pm will be delivered tomorrow

Your Address

Product Description

Part Number:
13321

Adapts "Quick-Connect" 4-way Piggyback to a 7-Way plug.

  • Simple plug-in connections.
  • Industry standard wiring configurations and color codes.
  • Retains 4-way flat Piggyback for use with all U-Haul trailers and common boat trailer wiring.

Questions & Answers (9)

To view an answer to a question, simply click on the question. To post a new question, click on the "Ask a question" button below.

Ask a Question

*All questions are reviewed and approved before being posted or answered.
Please keep all questions appropriate and related to the product

will this adapt my existing 7-way receptacle to a u-haul 4-way flat trailer plug?

–kelly 2/19/2014 7:22:18 PM

Our hitch pro writes: "13321 is designed to adapt the 4-flat vehicle end to a 7-way flat pin connector. If you are planning on towing a U-Haul trailer and your vehicle is equipped with a 7-way flat pin connector, please use U-Hauls 47335 7-way to 4-flat adapter. "

–Ronald 2/21/2014 9:32:09 AM

If im just using the 4 flat to seven round adapter for indicators brake lights and marker lights , do I have to connect the white ground wire thats on the adapter?

–Barry 5/2/2014 2:16:02 AM

"The white wire will need to be grounded on the vehicle to function properly." ... as noted by our hitch pro.

–Ronald 5/5/2014 10:05:16 AM

I have attached the 4-way (U-Haul installed) from the vehicle to the adapter and grounded the adapter but the lights on the trailer still do not work. What are the other two wires from the adapter supposed to attach to?

–Dan 9/11/2014 11:29:53 AM

"The 13321 4-flat provides the 7-way with stop, tail and turn. White wire - Common ground. Blue Wire - Electric brake. Black Wire - Battery charge. Yellow - Auxiliary. (more commonly for reverse light). If you are not getting any trailer lights after plugging in the 4-flat and grounding the white 10 gauge wire, please schedule an appointment with your local U-Haul hitch professional who can quickly diagnose and repair your wiring issue."

–Ronald 9/11/2014 3:46:21 PM

What what colors do I collect

–Jose 12/16/2014 1:18:14 PM

4-flat provides Stop, Turn and Tail lights. White wire (Ground) - Connects to a clean surface on the vehicle frame. Black Wire (charge line) - Connects to vehicle battery with in-line breaker, most commonly used to charge trailer battery. Blue Wire (brake control out put) - Connects to vehicle brake controller out put wire. Yellow (Auxiliary) - Most commonly connects to the vehicle reverse light to release trailer surge brake when backing up.

–Ronald 12/16/2014 3:44:26 PM

Currently I have a “T” connector wire harness hooked up to my mini-van. If buy I this adapter would that mean I would have 3 wires running to my battery? First one for the existing “T” connector, second for the black wire in this kit and third for the yellow auxiliary in this kit? I believe I need the yellow auxiliary to run the 12v stuff on my trailer, but what does the black wire power as the “T” connector already has power going to it?

–Kevin James 4/15/2015 11:51:12 AM

The 13321 12v trailer battery charge line (black wire) must be ran to the vehicles battery with an in line circuit breaker (U-Haul part 13520 or 13530) separate from the 4-flat module battery feed.

The 13321 center auxiliary post (yellow wire) is more commonly connected to the vehicles reverse light for releasing a boat trailers reverse lock out solenoid. However, can be used as another 12v source if needed by running an additional wire and in line circuit breaker to the vehicle battery.

–Joseph 4/16/2015 10:40:00 AM

I have a 4 way on the back of the U haul truck I purchased, my trailer is a seven way plug, what do I need to connect them?

–Becki 10/30/2015 6:49:36 AM

Both 13321 and 47185 will adapt your 4-flat to a 7-way spade.

Tech tip: The 13321 & 47185 12 gauge white ground wire must be grounded to the vehicle for proper lighting.

–Joseph 11/2/2015 3:41:26 PM

Have pop up trailer with 7 round plug and truck with 4 flat. Will this connect work

–Richard 7/10/2017 5:16:13 PM

Hi, Richard! Once plugged in and white ground wire grounded, your trailer will receive turn signal, brake lights, and running lights from the truck 4-flat.

If you require further assistance, please contact your local U-Haul Hitch Center. I hope that is helpful!

–Savannah 7/28/2017 4:19:24 PM

Is this the right part for my 2014 Nissan frontier

–Ed Hatfield 7/13/2017 1:04:00 PM

Hi, Ed! The 13321 is a universal, pre-wired 7-way trailer connector designed to plug into a vehicle's existing 4-flat trailer harness.

For more information on vehicle specific 7-way connectors, please visit your local U-Haul Hitch Center. Thank you!

–Savannah 7/28/2017 4:27:12 PM

Where are the wiring instructions?

–Pac Zachary 8/30/2018 5:30:51 PM

Hello, Pac! Here are the wiring instructions:

  1. Determine a suitable mounting point on the tow vehicle for the adapter. Make sure that the trailer's wire harness has adequate length to reach this point and mount the adapter.
  2. Plug the 4-flat plug of the adapter onto a 4-flat plug extending from the vehicle. This will provide tail light, left and right turn functions.
  3. Locate a grounding point near the adapter such as the vehicle's frame or cross member. Clean dirt and rustproofing from the area. Secure white wire with the eyelet (do not drill into vehicle floor or bed).
  4. Connect remaining wires by crimping yellow connectors (see image above for a diagram of wire locations).
  5. Note: white wire in 4-flat is not connected to the 7-way adapter. The large white wire must be grounded to assure proper trailer light function.
. Thank you!

–Savannah 8/31/2018 1:20:37 PM

Recommended Items