How to Wire Electric Brakes on a Tandem Axle Trailer

Question

Question:

Installing new trailer brakes on a tanden axle trailer.When wiring my understanding is that the existing 7 pole wiring can be tapped into by running a two wire 12 guage section from brake to brake and then splicing into the existing 7 ptong and attaching the blue and whiteground wires.Do i have to ground the white wire to the trailer ? Thanks

asked by: Gene L

1

Helpful Expert Reply:

If your trailer has 7 wires running all the way back to the brakes, then yes, you can tap into the existing wiring. Each of your new brakes will have two wires for the brake magnet. One wire is for 12 volt power to the brake magnets and the other wire should be grounded either to the trailer frame or to the main trailer ground wire. It does not matter which wire is used for power or ground because they are not polarized.

If the trailer wiring is running down the left side of the trailer, then we splice the left side brake assemblies into the main electric brake power wire coming from the 7-way connector. We then run a jumper wire from the electric brake power wire to the right side brake assemblies (see photo).

I recommend using 12-gauge wire, # 12-1-1, for the jumper wire and for additional ground wire. If you want to use duplex wire, you can use part # 10-2-1.

I have attached an electric brake installation video for you to check out. The trailer in the video is a single axle trailer, but it will give you an idea on the installation process.

expert reply by: John H

1

click to enlarge

Matt

2/23/2020

Bought a tandem trailer with brakes on one axle. Axle tube has 2 wires coming out on both left and right sides. Are these suppose to be connected to the brakes on their respective sides? What is the wiring diagram? Never seen wires coming from inside axle.

Chris R.

2/25/2020

I have to assume the two wires coming from each side of the axle on your trailer are for electric brakes only because I'm not sure what else they would be used for. I haven't really seen that before either but there are lots of fun ways a trailer can be wired up.....Just to be sure you could try testing them with the brakes activated when hooked up to the tow vehicle to see if one gets power (one will be for power and one will be for ground on each side).

Glynn J.

1/25/2022

@Matt the double insulated wires are generally in the hollow axle to protect them. They exit on each side. The magnet on the side with the wire harness will have a blue wire and white wire to connect to the magnet and also the wire through the axle will have a white and black wires to connect.

Gene L.

3/28/2025

@ChrisR Hi There, I have a 2013 Venture 19 foot Ultra lite dual wheel TT, How many feet of wire (approx.) will I use or need to buy to replace the old wires for the dual wheel electric brakes? I figure I may need 20 30 40 feet? OK Everyone sells it by the foot and trying to get a one piece for the full replacement. Thanks Gene

See All (4) Replies to Matt ∨

Mike B.

6/11/2020

I am having a brake problem on my TT. I keep getting a message in the truck that the trailer brakes have disconnected. it is intermediate. I disconnected the blue wire and ground wire for the brakes and tested each to ground. I have continuity on the blue wire to ground with the brake ground wire disconnected. This does not seem normal to me. What is your opinion?

Jacob H.

6/15/2020

This sounds like you may have corrosion and/or a bad connection on the pins of your 7 way plug either on the vehicle or the trailer. I would check to make sure that the connection is not loose and that the pins are clean.

Mike B.

6/15/2020

@JacobH I found the problem a few days later. One of the magnets had an internal short. Replaced the brake assembly, problem solved!

Chris R.

6/19/2020

@MikeB Yes!

Answer 1

It sounds like you are speaking of the wires for the brake magnets. If this is correct, you will need to connect one of the wires to the brake controller output wire on your trailer connector and the other wire will need to be grounded to a clean…

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Answer 2

There really isn't a particular maximum trailer weight that is used to determine when brakes need to be added to both axles of a tandem axle setup. While I do still recommend checking your local laws, I am also not aware of any general laws that…

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Answer 3

You can definitely add brakes to an axle without purchasing another one. The easiest thing is if your axle already has a brake mounting flange installed on it. If your axle doesn't then you can have one welded on, but we typically recommend…

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Answer 4

That's a very good question, we tend to be extra cautious and say to use 10 gauge wire because that would be more than enough. When you get into longer trailers that will end up using a lot of wire the heavier gauge wire becomes more necessary.…

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Answer 5

In some situations, brakes can be installed on only one axle of a tandem axle trailer, however you should first check your state laws to see how many brakes are required for the gross vehicle weight rating (GVWR) of your tandem axle trailer. Some…

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Answer 6

The studs on the Dexter 7 inc brake assembly, part #23-47, are 1-1/4 inch long with 7/16 - 20 threads. Brake Assembly mounting bolt, part #7-75, is 1-1/4 inch long with 7/16 - 20 threads. The nuts, part #6-17, are also 7/16 - 20. This size is pretty…

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Answer 7

Jameson is correct - on a tandem axle trailer you want brakes such as the Dexter Nev-R-Adjust Electric Trailer Brake Kit - 10" - Left and Right Hand Assemblies - 3.5K #23-468-469 on the axle that bears the most weight, and in the large majority…

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Answer 8

Yes, you can jump the front axles brake output circuit to power the rear axle. Check out the picture I attached to see how most people do this.

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Answer 9

The brake wire providing voltage is wired in parallel, with one lead from each magnet being grounded to the trailer frame. We have a great Wiring Help Page that shows a diagram, I will provide a link to it below.

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Answer 10

Normally a tandem axle trailer only has one brake wire going to the vehicle, and it is typically blue. If you have two separate brake wires for your axles, that is fine and will not cause an issue. Having one wire ran along the trailer instead of the…

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Answer 11

The right and left orientation is determined if you are standing behind the trailer looking towards the tow vehicle. The left side is the drivers side and the right side is the passengers side. Tthe shorter brake pad will always be in the front of…

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Answer 12

Going by the colors that you mentioned, it sounds like you have the typical set-up, green wire for right turn and brake, white wire for ground, yellow wire for left turn and brake, brown with green wire for right side running lights, and brown with…

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How to Wire Electric Brakes on a Tandem Axle Trailer

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