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.

Reply

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).

Reply

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.

Reply

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

Reply

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?

Reply

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.

Reply

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!

Reply

Chris R.

6/19/2020

@MikeB Yes!

Reply

Answer 1

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…

view full answer...

Answer 2

If you are referring to two white wires from the brake magnet that are coming from the rear of each electric brake assembly, then it would not matter which wire is connected to ground and which wire is used for the brake feed. The magnet that…

view full answer...

Answer 3

Hello Blake, thanks for reaching out. I did some digging and I was able to find a reference for the 92655 hub. This uses the 15123 inner bearing and 25580 outer bearing. It will be a 12" drum as well. This reference didn't tell me the bolt…

view full answer...

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.…

view full answer...

Answer 5

If you are wanting to go to higher capacity leaf springs I would advise against it. The problem is that since the trailer axle is rated for 3,500 pounds you won't gain any additional capacity by switching to higher capacity springs. What it will…

view full answer...

Answer 6

We don't have a way to look up the length of your leaf springs as that's not something that a record was kept for. But I can say that nearly every 3,500 lb axle spring out there needs the 25-1/8 inch replacement like the part #e54SR so while…

view full answer...

Answer 7

Typically trailer wiring is color coded. The brake circuit is usually a blue wire which travels to each brake magnet, where it is attached to one wire from each brake magnet. The other wire from each brake magnet will ground to the trailer frame. I…

view full answer...

Answer 8

First you will need to remove the old hydraulic equipment. Remove the surge coupler or actuator, remove all the lines, and finally remove the brake assemblies. If you have 10 inch diameter hub and drums, you may need to replace those as well. If you…

view full answer...

Answer 9

Hey Zach, congrats on the new trailer! You can either look at the info sticker near the tongue of the trailer to find the weight ratings of each axle or, if you can't find that, there is a sticker in the middle of each axle showing what the…

view full answer...

Answer 10

Hey Chris, thanks for getting in touch. The plug in your picture is known as a 7-way round pin connector. If you are wanting to keep the wiring on the trailer as-is, and you just want to swap out the plug for a standard 7-blade, it will definitely be…

view full answer...

Answer 11

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…

view full answer...

Answer 12

I reached out to Dexter and even with your axle tag they do not have any information on your axle since the it was ordered as a beam. In order to find if the Bearing Kit, 15123/ 25580 Bearings, 10-36 Seal #BK3-100 is the correct replacement, you will…

view full answer...

How to Wire Electric Brakes on a Tandem Axle Trailer

Products Referenced in This Question

Product Page this Question was Asked From

Featured Help Information

Miscellaneous Media

Continue Researching