How Does a Brake Controller Know when a Trailer is Connected

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Question:

Good morning, question is what signal is the brake controller receiving when trailer plug 7 wire is plugged into the vehicle

asked by: Marv

1

Helpful Expert Reply:

When a trailer with electric brakes is connected to a vehicle that has a brake controller that brake controller is sensing the draw of the brake magnets by sending back a small amount of voltage on the blue wire.

The brake controller also get's signals from the tow vehicle to let it know when you are stepping on the brake pedal. On most vehicles this connection is made either at the brake switch above the brake pedal or through some kind of tow package wiring.

I have included a link to our help article on brake controllers for you. It covers proportional and time delay controllers. If you are in a market for a controller I recommend a time delay such as the P2, # 90885. Proportional controllers activate the trailer brakes in proportion to how much the vehicle is braking using internal sensors. This is the safest way to stop and it reduces wear and tear on the vehicle and trailer.

expert reply by: Michael H

1

Jim W.

3/29/2020

I have a Hopkins Agility Brake Controller about 2 years old. The controller worked up to about a month ago indicating the trailer was connected. The red lamp that indicates this stoped working. The controller has voltage and ground from the battery and receiving voltage from the brake peddle. Blue wire good from the controller to the battery connections that stops a brake away trailer. Would one magnet cause the indicator to disappear or the brakes on the trailer to stop working?

Reply

Chris R.

3/31/2020

A bad brake magnet could be enough for the controller to sense a lost connection, since their draw is what is used to detect this. If you found that the brake magnet is bad, it certainly wouldn't hurt to replace it to see if it resolves the issue since it need to be done, anyway. Also check the power and ground wires coming from each brake assembly to make sure they're still securely attached - these (especially the ground wire) can come loose over time.

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Alice

5/2/2024

I have no brake lights with no trailer connected, how can I fix that

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Answer 1

To install a 7-way in your 2010 Ford F-150 with a factory 4-way all you would need is the #37185. This will plug into the 4-way you currently have and will give you both a 4-way and a 7-way at the rear of your truck. To complete the 7-way wiring you…

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Answer 2

You can use 14 or 16 gauge wire for your marker and tail lights on your camper. I recommend using the Deka 14 gauge jacket wire #DW04923-1 because it's insulated for abrasion and chemical resistance. Having more marker lights means more draw on…

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Answer 3

Aftermarket brake controllers send a small amount of voltage along the brake output wire, if a trailer is connected, the magnets in the brake assemblies will create a power draw. This power draw tells the controller that a trailer is connected. The…

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Answer 4

I will be happy to explain how to install an electric brake controller in your dump truck. First, if the truck does not have a trailer connector at all you will need to add a 4-Way first. If the truck has the brake lights and turn signals on the same…

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Answer 5

All the brake controller needs to sense a trailer connection so that you can test it is a slight amperage draw on the output circuit. For that you can use a circuit tester like the part #PTW2993 with one pin grounded and the other on the output pin.…

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Answer 6

I can help you with greasing up your EZ Lube Axle. First thing I would check would be that the grease is not coming out of the back of the axle through the seal. If this is the case you will need to replace the seal. Our tubes like #L11390 have 14…

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Answer 7

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 8

The "Trailer Disconnected" error message on the dash with a factory brake controller is usually related to an issue with the blue brake output wire that runs from the brake controller to the 7-Way connector. The fact that the issue remains…

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Answer 9

I have included a link to a video on adjusting self-adjusting brakes. Basically there is a device on the adjustment wheel on these brakes that prevents the shoes from adjusting back inward. You have to sort of move that out of the way to be able to…

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Answer 10

Assuming that when you tested the resistance of the brakes you were testing the two wires on each magnet and getting 2.0 and 2.8 ohms the magnets on your trailer are not working correctly and will need to be replaced. For 7" brakes you should…

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Answer 11

I am not entirely sure what process you took so I'll give you some other things to try, or maybe a different way to test the Prodigy P3 #90195. First, sever the blue wire a couple inches from the back of your controller. Then use a circuit tester…

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Answer 12

That will depend on the amount of brake axles your trailer has. . The 20 amp breaker like #9506P is for 1 and 2 axle brakes, and the 30 amp like part #38630 is for 3 and 4 axle brakes

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How Does a Brake Controller Know when a Trailer is Connected

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