Troubleshooting Weak Trailer Brakes That Won't Lock Up with Override Lever of Controller Slid

Question

Question:

I can not get the brakes to lock up with the manual slide override. I max it out @ 12 volts but the trailer brakes barely have any stopping power. I tried setting them up just as the instructions said but they will not work.

asked by: George M

0

Expert Reply:

This could be a magnet wiring problem. It is unlikely that the magnets are bad on newer assemblies, but if the wiring is not properly connected, it could cause problems. Check to see that the magnets are properly grounded to a clean, bare metal surface free of corrosion. A bad ground would not allow the circuit to be complete and lead to the brakes not performing like they should.

I also recommend checking the trailer side connector ground and the vehicle side connector ground.

Another possibility is that the brakes are out of adjustment. You want to adjust the assemblies so that there is a light drag when the wheel is turned. To see how this is done check out the video I attached. Fast forward to the 4:30 mark.

I also attached an FAQ article on troubleshooting brake magnets.

expert reply by: Jameson C

0

Jason H.

4/27/2020

we just installed new brake assemblies on all four corners of a 20 flatbed trailer. All wiring and contacts are good. No grease. Nothing. When we run the trailer gain up to 10, the trailer BARELY holds the 5.7L gas pickup truck. We run across gravel and slam the controller on at 10 and the wheels refuse to lock. What could be wrong ?????

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Chris R.

4/29/2020

Are the new brake assemblies self-adjusting units, by chance? If so - there is a period of "adjustment" that still needs to take place after they're installed. This really just consists of driving around an empty parking lot and braking at various speeds. Each braking episode will adjust them further towards ideal operation. If they're manual adjustment assemblies, make sure they're properly adjusted according to the video Jameson mentioned above. If this is all good then there could be an issue with the brake controller or wiring on the truck - let me know what you find and we can dive into that if needed.

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Robby

6/6/2020

I been having problem with a brand new set of brakes . They are adjusted all the way up and will not stop trailer . I have battery voltage at the new magnet assembly . All wiring is new and extra good ground is has been added . The only thing that is not new is the drums . The drum were not scored and smooth . Could the new magnet brake assembles not expanding enough for the old drums ?

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Flanagan

7/10/2020

I too have lost my trailer brakes I greased the ball hitch recently Could this be the problem ? Wiring all checks out

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Chris R.

7/14/2020

I wouldn't think greasing the hitch ball would have any effect on the trailer brakes. I would start by testing the 7-Way connector on the tow vehicle to see if you get power at the brake output pin when pulling the manual override on your brake controller. We need to pin down which side the issue is actually on - the vehicle or the trailer. Let me know what you find and we'll go from there.

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Harold

7/9/2024

I'm surprised no one said anything about the voltage. Many of these cheaper brake controllers won't even get up to 12 full volts therefore will never lock up the brakes. If you only have 9.5 volts the trailer brakes will shut a little bit but they're better going to close and lock up all the way unless you have a full 12 volts and most likely when people buy a brake controller they go cheap and they get cheap. They need to put out a full 12 volts before the brakes will ever Fully lock up. I just had this problem. It works only put out 9.56 volts on the top end and lowering it was a joke

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Jameson C.

7/9/2024

@Harold Where were you measuring the voltage at? It's not uncommon if too light of gauge wire was ran back to the brake assemblies on the trailer wiring and there's a voltage drop. 10 gauge wire like part # 10-1-1 is needed here.

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Harold

8/7/2024

@JamesonC have the proper wire size run. I check it right at the controller itself. I spent a little bit more money and got one that works. I'm finding these days things you buy cheap you'll get cheap. Problem solved it just cost more that's all. I'm finding these days no since in buying cheap cause that's exactly what you're going to get cheap Junk

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Jameson C.

8/7/2024

@Harold Makes sense! It sounds like the cheap controller just didn't have the amperage needed.

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See All (5) Replies to Harold ∨

Harold

7/9/2024

Does this page even work

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Jameson C.

7/9/2024

@Harold Yes it does?

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Ray

8/7/2024

@Harold ever get an answer to this problem

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Jameson C.

8/7/2024

@Ray I answered his question if you scroll down further?

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See All (5) Replies to Harold ∨

Carlb

12/8/2025

Tekonsha 90160 IQ controler, With the manual fully applied I cant seem to get the trailer wheels to lock . I have a 7X12 dual axle trailer with a 2017 Ford explorer with a factory class III package I recently installed the controller with the 303500 custom harness to the factory wiring. I then followed the instructions on initial set up and could not , even at 13 gain , get the trailer brakes to manually lock. I sent the trailer to a local trailer shop and had the breaks gone through and adjusted . The trailer was bough used (2023 manufacture date ) and the trailer shop said everything looked relatively new and seemed to be functioning properly. They did say they the breaks were quite a bit out of adjustment. After I picker the trailer up the response was better but even at 13 (FULL) gain they wont lock. I should be able to get the breaks to lock with the manual engaged, right? any ideas?

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Jameson C.

12/8/2025

@Carlb Brakes should be able to be locked up by a controller but it's actually not the best to have them set so strong they will lock up so while maybe there is more braking power you can get out of your setup you won't want to lock them up. Did anyone mention burnishing the brakes? Have you checked the wiring to the brakes to make sure they are 10 gauge?

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Carl B.

12/9/2025

@JamesonC Thank you for getting back. I have not checked the wiring gauge, I will. Keeping in mind that the truck has a Ford factory Class III package and the trailer is 2 years old have you heard of instances where a trailer came from the factory with the wrong wire gauge? The local shop that went through the brakes ( I have confidence in the shop they are considered the one of the best locally) did not mention any drum glazing or compromised pad material. The locking by manual control is indicated as a starting point for the gain adjustment in the instructions for adjustment. I assume that if I cant achieve this there is a problem. Question: is gain value on the controller display the "voltage" I should be reading at the 7 pin? For example if the controller gain value is set at 6 and the manual is applied fully should I get a voltage reading at the 7 pin of 6 volts , if the gain adjuster is set at 13 should the voltage reading be 13 etc. If this is the case I could quickly eliminate the truck by milti meter readings and focus on the trailer. Any thoughts? Thank you again for the help I really appreciate it. Carl

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Jameson C.

12/9/2025

@CarlB Yes, the number on your controller output would be the same as the voltage that should be coming out of the back of the controller. Sometimes there is a bit of voltage drop from the controller to the 7-way though so that would be normal if you found that. Brake burnishing is a process to basically break in the brakes so that they can grab to their full potential. I attached a link that covers this process. Generally a new trailer should have the correct gauge wire but weirder things have happened...

Helpful Links

faq-adjust-trailer-brakes.aspx

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Answer 1

Since the trailer was off of the ground it would not take much voltage to stop the wheels from spinning so they may be getting power but they may not be getting enough power due to a short or wiring issue. But 9 times out of 10 weak trailer brakes…

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Answer 2

Try also checking the relay in slot 37. On your 2019 Ford F-250 the 27 and 37 slots of the fuse box/relay box controls the 12 volt trailer wiring circuit of the 7-way. Otherwise you may have damaged wiring with the short you created.

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Answer 3

The brakes should still work fairly well. The magnets, when energized, cling to the armature surface of the drum and the rotations of the drum pull the magnet which then pushes out the shoes to make contact with the drum. If the brakes seem weak then…

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Answer 4

Thanks for reaching out! The correct tee fitting you're looking for to install the Demco Air Force One #SM99243 on your Freightliner Super C chassis is found as this on our site - Replacement 0.5" Pushlock T-Fitting for Demco Air Force One…

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Answer 5

A dead battery would not be the cause of your brakes not disengaging. A dead battery would have the complete opposite effect on your brakes. A dead battery wouldn't send the electric signal to engage the electric brakes and no electric signal…

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Answer 6

Sounds like your brake controller will apply your trailer brakes if you apply the manual override lever but not when you press the brake pedal. This is a fairly common problem and the solution is the red wire of the brake controller. Make sure it is…

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Answer 7

The brake assemblies you have are 7k Dexter assemblies that are 12 inch by 2 inch in size. The part number #AKEBRK-7-SA will work as a great replacement set. This includes assemblies for both sides of your trailer that are self adjusting.

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Answer 8

The Camco Water Heater Element - Screw-In - 1500 Watts - 120 Volts #CAM02143 has been proven to work on your Suburban SW12DEL water heater. The length is on 6-1/4 inches with the thread diameter portion a 1-1/4 inches. I've attached a photo to…

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Answer 9

It sounds like you're looking for the Dexter Trailer Axle Beam part #8327816 which is 86.5" long at the hub face and has a 5,200 lb weight capacity. The spring seats however will need to be moved in for your application which requires tack…

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Answer 10

Actually, there's a little more to it than that. The magnets on the #K23-478-479 are a little different, but the primary difference is the mounting bolt pattern. On a typical 3500 lb brake assembly, the mounting studs will all be 2-7/8 inches…

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Answer 11

The correct hub/drum for a Dexter 4,000 Lb Axle is the Dexter Trailer Hub and Drum Assembly part #K08-426-91. Then for the brakes, you can use the Dexter Nev-R-Adjust Electric Trailer Brake Kit part #23-468-469. The hubs/drums for a 3,500 lb axle are…

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Answer 12

The humming sound you hear from your trailer's electric drum brakes is a good sign. It means that the brakes' magnets are being energized by the output from the trailer brake controller in the vehicle. The issue with the brakes not applying…

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Troubleshooting Weak Trailer Brakes That Won't Lock Up with Override Lever of Controller Slid

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