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

Alice

5/2/2024

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

Reply

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?

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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.

Reply

Answer 1

Your problem is in the wiring in one of two places. It is either on the vehicle wiring harness or somewhere in the wiring on the trailer. The first thing to do would be to narrow it down to one of these two places, then we can pin-point the problem…

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Answer 2

The magnet clips #BP19005 should not be making contact with the drum while the brakes engage, so I do not think that is the problem. What I think is going on is it's just not seating all the way. These can get a little squished or deformed…

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Answer 3

If the controller is working fine with one trailer and not with the other then the problem is most likely with the trailer and not the truck. I would start by checking all of the ground connections on the trailer, especially the ground at the coupler…

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Answer 4

We don't have the length of stud you are seeking. The longest 5/8 inch stud we have is 3-1/8 inches. If that length will work, I recommend the Replacement Trailer Hub Wheel Stud, Drive-In, 5/8" x 3-1/8" (Qty 4) #RG03-120. These are a…

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Answer 5

To determine why you do not have any power on the blue brake output wire, I recommend starting at your brake controller. First, make sure the brake controller is on and receiving power. Most brake controllers have 4 wires, blue (brake output to…

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Answer 6

There are a number of reasons why the brakes on your trailer may not be working. Lets start with the easiest things to check. First, check the vehicle and trailer connectors for corrosion. This can cause a short inside the connector and the brake…

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Answer 7

To add electric brakes to your 2006 Starcraft pop-up camper, there are a few bits of information you'll need to know. Instead of measuring your axle, you would need to know its weight capacity, as well as the size of your wheels, your mounting…

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Answer 8

To cover the easiest things first, make sure that the brake controller output or gain is turned up. If the power is low then the voltage on the blue wire will be low. When testing for voltage make sure to use the manual override and not the brake…

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Answer 9

Brake magnets for 12 inch brake assemblies should have an ohms reading that falls within the range of 3.0 to 3.8. The 3.7 ohms reading on your brake magnets does not indicate that the brake magnets need to be replaced. If you are experiencing…

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Answer 10

The trailer tire and wheel part #AM32182 would work great for you as this is exactly what you have now.

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Answer 11

The blue wire on a brake controller is output to the trailer brakes. If that wire is not connected the trailer brakes will not be getting any power. If there is a break in that wire somewhere between the controller and the trailer connector then that…

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Answer 12

I have attached a photo for you below which shows how both a vehicle side and trailer side trailer connector is typically wired. I say typically because this is not always exact and so long as the trailer and vehicle side both match it will not…

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How Does a Brake Controller Know when a Trailer is Connected

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