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

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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?

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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.

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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!

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Chris R.

6/19/2020

@MikeB Yes!

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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.

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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).

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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.

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Answer 1

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…

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Answer 2

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…

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Answer 3

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…

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Answer 4

That&#39;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…

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Answer 5

Something might got miss-wired most likely when you replaced the old 7-way with the part #H20046. Since there are two different color codes for 7-way trailer wiring this isn&#39;t super rare. Check out the diagram I attached that shows how…

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Answer 6

You are super close to having the brakes functional on your trailer. Run the blue wire from the brake output pin to either one of the wires that are coming off of the brake assemblies and then ground the other and you'll be done. Brake…

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Answer 7

To be frank the only difference you will really notice going to a larger ST225/75R15 tire with a load range of E over a ST205/75R15 tire with a load range of D is in your wallet. Slightly larger tires with a bit more capacity are going to cost you…

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Answer 8

If your Bulldog Powered Trailer Jack like part #BD500199 is operating in reverse (up is down and down is up) then most likely it is indeed just a matter of switching the wire leads coming from the switch. This should resolve the issue. If this does…

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Answer 9

EZ Lube axles like the item #T3584F-EZ-8974 come from the factory with just a little bit of grease in the bearings. The first time you use the EZ Lube feature to fill the axle, it will take a lot of grease. You will probably use 3/4 to a full tube…

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Answer 10

Your Dexter D120 axle is rated for 11,999.80lbs, has a spring center measurement of 45.5" and track width of 74". It is an underslung axle that uses 3" wide 30" slipper springs rated at 6,000lbs each. The brakes…

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Answer 11

If your trailer is currently equipped with electric-over-hydraulic drum brakes then a good portion of the conversion process to change it to an electric only brake setup will simply be removing existing components that are no longer needed. You…

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Answer 12

You can indeed test a trailer's electric drum brakes by directly applying +12V power from a fully-charged battery. You can apply this power to the hot and ground contacts on the trailer's plug (see photo please) or to an individual…

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How to Wire Electric Brakes on a Tandem Axle Trailer

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