"Check Trailer Wiring" and "Trailer Brakes Connected" and intermittent loss of trailer brakes

[Boudicca908]

Last September (2025) I mentioned this issue in another thread, and said I would post a new thread when I had it resolved. The thing is -- I don't have it resolved.  I've been chasing this for months, unhappily. So I am going to share the saga, I will try to boil it down into concise bits, and maybe some of our more mechanically inclined members will have some ideas and suggestions. 

TV is a 2023 Chevy Silverado HD 2500 diesel truck.  Oliver is a 2022 Elite 2, bought new from OTT.  

In early September 2025 I needed new tires. I dropped my truck off in the late afternoon at a reputable place in Pinedale WY. I asked them to check the spare while they were working on it. The following morning they called to inform me that my batteries were dead, so I needed new batteries as well. The next afternoon I picked up my truck; by the time I arrived back at camp, it was getting dark. I shut off the truck and discovered they had turned on my overhead lights and left them on (hence my dead batteries?)... In the morning I hooked up to tow to my next destination, and began getting alternating warning messages on my dashboard and center console: "Check Trailer Wiring" and "Trailer Brakes Connected" 

I pulled over (not 5 miles from camp) and checked my 7 pin connector; it looked clean, was firmly attached, my trailer lights all seemed to be working. But the messages continued.  I could 'dismiss' these messages from the steering wheel, but they would pop back up immediately and they interrupted my view of my map on the center console, making it difficult to follow. In Denver CO, I had 10 days with family. I was convinced that something had happened to my wiring under the truck near the spare tire (wires, modules all in proximity.)  I took my truck to two Chevy GM dealerships; neither had time for me nor would they allow me to bring the TT on site, but each ran their diagnostic and both came up with these history codes: 

B1325 Control Module Power Circuit Low Voltage, failure code 0x03;  C1114 Trailer Brake Control Solenoid Valves Control Circuit, failure code 0x00; and P0562  Voltage Low, fail code 0x00. 

I call ahead to Amarillo TX dealership, explain the situation, guy on phone says he knows exactly what is wrong. Make appt. They don't do anything on Friday except change the oil; then the electrical guy is off for the weekend. I finally get the truck the next week, with this description: "Verified concern. Connected scan tool, found DTC C114 set in chassis control module, Checked trailer 7 pin connector for signs of corrosion, none found. Removed connector x188 at trailer receptacle and inspected for worn and pushed out pins, everything OK. Placed test lamp at pic c to ground and commanded low to high percentage with scan tool. Test lamp followed command from low intensity to high intensity change in bulb. Internal malfunction in k133 trailer brake control module. Replaced trailer brake control module and cleared DTC. Test drove to verify message did not appear on dash."  (They did test drive the truck -- 18 miles worth.) $400 bill. I hooked up my Oliver to pull out, and the warnings continue. All during this time, my trailer lights and brakes seem to be working fine, but the warning messages continue.

Fast forward to February. I hooked up for a short camping trip in Florida and the messages return.  **I should note: I can't keep my OTT at home, and it's in a storage facility about 50 minutes north of my home. I'm not allowed to 'work' on it at the storage facility, and I can bring it on site to my neighborhood but only for a few days each year.**  I call OTT Service dept on May 3, to check their calendar in case I need to come up before I head west for the summer; they have openings both spring and fall. I am determined to dog this thing and to try to resolve it without having to tow 900 miles to Hohenwald before my trip west. 

I have now taken the truck to 4 dealerships. They all say, "It's the trailer."  I take my truck to an independent mechanic and he says, "It's the truck, but the modules should be under warranty, so go back to the dealer for this."  Just to be sure, I find a Mobile RV Tech, tow the OTT to my neighborhood for one night, have him do his service (everything checks out fine on OTT, all working, but he finds something loose under the truck and the messages go away. But then they came back. This is exhausting. 

May 2026 -- Issue was still there, and now my trailer brakes aren't working. That is a new symptom. I say not working, but it was really intermittent; I could test with the gain control on center console and sometimes working, sometimes not.

June 3, 2026 -- Back to dealer (45 minutes north of me), "It's the trailer."  This time they let me bring OTT in tow; but they still say, "It's the trailer."  A friend suggested another independent diesel mechanic that happens to be near the dealer.  From the dealership I towed OTT to Elite Diesel in North Fort Myers, it's 3:30pm. They make a cursory review for about an hour, and say they believe it's the truck. 

June 4th, 2026 -- At this point, I am nearing departure date, so I haul trailer home, take truck back the next morning, get a ride home. Within 30 minutes they call me, "Can you tell us why your left side truck battery ground wire isn't connected? It still has the black cap on the end that it's shipped with, the cap on end of ground cable was never removed from the cable."  (I've made 5 visits to  Chevy dealerships citing need for regular service AND this electrical issue and NONE of them noticed this?)  My new mechanic thinks this has solved the issue. I get ride back up (45 min), retrieve the truck, drive home (45 min), connect the trailer, issue still there. I tow the truck and trailer both back to independent diesel mechanic (45 min).  I have work I need to do on my Oliver, so the mechanic agrees to let me do my work there (greasing my zerks in his parking lot) while they disassemble the spare tire, remove modules, check wiring in back of truck..... Now they are thinking something must be amiss in the trailer wiring. They don't stock that cable, so I might need to order one. I call OTT Service to inquire about what model or brand Oliver uses, since I've read that they are not all alike; Mike says he can't help me, transfers me to Tech Support. 

Jerry at OTT Tech Support talks to me about the 7 pin cable. He says the 7 pin cables are really the same (but Chevy Service Manual warns to use the "right one" to correctly operate the Chevy.)  Jerry gives me some solid advice -- don't let them cut the head off the 7 pin connector; if head needs replacing, take it back to the junction box under the vanity, and other tips.  I have no idea about this junction box; I can't find it in my manual or wiring diagrams, but I'm not a mechanic or electrical engineer.  Jerry sends me a series of photos that show the route of the 7 pin cable in the trailer to a junction box inside the vanity cabinet. (see below)  He says "if it has to go farther back from there, it's a really big job."  (Oh boy.) 

        

        

    

My mechanic removed the vanity panel -- immediately saw two wire connections are loose though still have the nuts on the connection (below).  ** I need to find the correct caulk (and thanks again to Jerry for providing the name of it) Silicone: ASI 335 Advanced Adhesion 100% Neutral Cure RTV Silicone, WHITE.  Until that is fixed, I won't be using my shower, since it's open to this electrical junction box.**

He tightened that down. Then he tried to find the rest of the wire, crawls under the trailer, sees wiring going into the street-side front axle where the insulation has been rubbed off. I am dumbfounded, so I wriggle under there, stick my head around the corner; these are really small wires, going through a hole in metal without any protection; they rub on that hole in the metal axle, and I see there is no grommet on the hole. This doesn't seem right to me. 

 

He wrapped it with electrician's tape. I drove around, and the issue had cleared up. I drove around some more. No warning messages. I had not crawled all the way under my Oliver before, though I have been greasing my zerks regularly; I grease the zerks from the side, not from below. I gave my phone to the mechanic and he snapped a couple of photos that I shared with Jerry, before he put the tape on. I was ecstatic, and so happy that with 3 distinct wiring issues this mechanic was willing to dog it, find them and deal with them. 

And THANK YOU JERRY.  This is June 4th. My reservations are all in place and I depart early on June 8th. 

Yesterday June 10th, I called OTT Service again to inquire about whether there should be a grommet on that hole, and if so what size or could they ship them to me? Mike says he doesn't know if there should be a grommet, doesn't know the size and doesn't sell parts; transfers me straight to Tech Support.  I talk to Jerry -- my hero -- and I send Jerry the photo from my mechanic before it had electrical tape on it.  I had already purchased some Liquid Tape, extra electrician's tape and a box of Wire Conduit (that black plastic sleeve that is used all over the OTT).  At that point in time, I was not getting the warning messages any more, but I was not entirely convinced that the tape on the wires would hold up to thousands of miles of travel.  Jerry encouraged me to keep my eye on things, and I could get it repaired during my scheduled service in October on my way to the rally before I go back home to sw Florida.  Don't you know it, less than an hour later, the messages came back. My trailer brakes seem to be working, as well as my lights, but it's very disconcerting. 

I found a Walmart parking lot and spent about an hour crawling around under my OTT. I applied more tape, put on a piece of wire conduit (sleeve) and inspected the other 3 axles. (below - you can see OLD piece of sleeve on far right side, and my new piece of sleeve, and you can see Mechanic's tape and my additional tape which is shiny and not dusty.) 

   

Additional tape and new conduit sleeve (above) on the street-side front that the Mechanic repaired. 

Other axels -- I added tape to one, shoved the grommet back into the hole on another (below). 

 

 

PHOTOGRAPHS & CREDITS:   Wiring into axle (2 photos by Elite Diesel in North Ft Myers);  Routing of 7 pin cable (5 photos by Jerry OTT Tech Support); the rest are my own photos, including my junction box with loose connections and my wire at axle with question about missing grommet (2 photos I sent to OTT); and then my 'discovery' of the grommets on the other 3 axles yesterday. 

The warning messages continue though they are sporadic.  SO FAR the brakes are working (tested by using the gain control on my center console, when traveling slow speed). 

I'm inclined to keep going on my travels. I have an appointment with OTT Service in October. 

But I am interested in any additional input, and -- if for no other purpose -- I submit this for others who might have to figure out where that 7 pin cable goes and possible places to look. *I did try to search for other threads about this, but found none. I feel certain I've seen some comments about "usually trailer ground wire issue" but didn't find it. 

Thanks to all who have been in touch, and especially JERRY at OTT Tech Support for his kind and timely service. 

*** Please note: my wifi connection is via starlink and might be sporadic, and only when I'm not traveling. ***

 

Edited yesterday at 05:25 PM by Boudicca908
fixed dates

[topgun2]

5 hours ago, Boudicca908 said:

I have an appointment with OTT Service in October. 

But I am interested in any additional input,

Certainly that hole where your brake wire exit the axel SHOULD have a grommet.  However, as a number of owners have found out - the brake wires that run through the axle can "short" due to the insulation wearing off INSIDE the axle where you simply can't see it.  Mike Thompson (among others)  experienced this.  The good news is that the fix is fairly simply and inexpensive - run a new set of wires on the outside of the axel(s).  I'm sure that Mike (or others) would be happy to give you the details.

Bill

[Geronimo John]

Wow what a difficult time you have had.  Frustrating for sure.

I had a simular issue with my 2018 OE2.  Problem was the male 7-pin.  Art and I changed it out and it stopped the rogue errors like yours.  

Many owners have had problems with the brake cable inside the axles.  John Davies used the cable protection like you used and ran the cables outside the axle with a bunch of zip ties.  He ran it on the back side to protect it some from flying stones.

One thing to try is to hook up your trailer to a different truck and see if they get a problem as well.  But finding someone willing to do that would be difficult.

GJ

[Boudicca908]

1 hour ago, Geronimo John said:

But finding someone willing to do that would be difficult.

Yes -- I have a friend at home who actually suggested that, but I didn't find a person available to test it that way. However, once I arrive in NM where I am meeting another Oliver owner, maybe she will be willing to test that out. No matter the cause, those wires being subjected to rubbing at the axles is ... no good. I will look for Mike Thompson (or a post, if he made one here on the forum?)  I am not on facebook. 

[jd1923]

Wow, so many variables and it's more difficult when you have to count on service technicians, to whom are not all created equal.

Yes, all 7-pin cables are the same. And yes, you can replace male head only (OTT is not always right). GJ did his and I did mine, been fine for 2 years. Changing out the whole cable is a bit of work. On my hull it's connected under the front dinette, past the wastewater plumbing (see pic). But who knows on yours since OTT hires random installers year-to year. In the picture you showed of a residential junction box, I don't see the trailer cable, the large black coupler cable, spliced down like you see in my picture.

If you want to be absolutely certain whether your issue is the truck or trailer, take your truck to U-Haul and rent the cheapest trailer with a 7-pin connector! There is a lot less liability in doing this than borrowing a friend's truck or trailer, and less money than an hour of labor, shop rate at the Stealership! 🤣

See if you get the error message when towing the U-Haul trailer. The logic is binary. If it still shows the error, then it's the truck. Tow the trailer long enough and if it doesn't display the error code, then you have a wiring problem with your Oliver.

So, if it's the Oliver, the next thing I would do is to test the brakes. Pull the pin on the emergency brake switch (the little cable you connect when hitching). Then take a clamp ammeter to the streetside, under the wheel well where you see two wires coming out of the hull, going to the brakes. Clamp onto only one wire, either wire of the pair. The ammeter should read about 6A on both sides (front and back axles). If it does, then all your brake wiring is good, so you can rule that out. (Don't forget to replace the safety brake pin when done.) If this test fails, then you have wiring issues at the axles, but don't waste time there unless you must.

If the above test is positive, then connect the 7-pin coupler to your truck and run the same test. If it tests bad, then the brake wiring from the coupler back is bad (open) somewhere. Your next step would be to replace the 7-pin male on the Oliver. This will likely fix any Oliver-side issues. You don't really want to replace the entire cable unless you have too and OTT would likely charge a fortune to do this job.

If towing the U-Haul trailer showed an error message, then it's your truck. What a shame 4 GM dealers cannot properly troubleshoot and fix the products they sell. If it was me, in a heartbeat I would disable the factory brake controller. Pull the fuses for it, buy an aftermarket Tekonsha controller and run new wiring to the female 7-pin outlet on your rear bumper (this is what I did from the start, since my older truck does not have a factory controller). This would cost about $200 in parts and likely 2 shop-hours to install, ANY trailer shop can do this, has the parts, maybe even the same U-Haul dealer could do it. I'd rather go to the dentist for a couple extractions than make a service appointment with an auto dealer, OMG! 🤣 And your story certainly shows why.

Keep us posted and let me know if you have questions on anything I suggested.

Best wishes, JD

[Mike and Carol]

14 hours ago, topgun2 said:

Certainly that hole where your brake wire exit the axel SHOULD have a grommet.  However, as a number of owners have found out - the brake wires that run through the axle can "short" due to the insulation wearing off INSIDE the axle where you simply can't see it.  Mike Thompson (among others)  experienced this.  The good news is that the fix is fairly simply and inexpensive - run a new set of wires on the outside of the axel(s).  I'm sure that Mike (or others) would be happy to give you the details.

Bill

Intermittent trailer disconnect messages have happened to a number of owners.  My problem was worn wires inside the axle.  Bryan @SNY SD UP in ND identified this issue first and shared his solution.  Simply replacing those worn wires fixed the issue.  I did go through months of troubleshooting and having my truck checked and tested at the dealer.  The thread below is one of several on this topic.

Trailer Brake Disconnect Message

Mike

[Boudicca908]

1 hour ago, Mike and Carol said:

Intermittent trailer disconnect messages

Thank you very much for the linked thread!  Will read it when I get to my next destination later today. In process of breaking camp now and hitting the road. :) 

It's interesting that my messages never reported Trailer Disconnected (except when I unplug the 7 pin connector, of course). My messages have always come as the pair:  Check Trailer Wiring AND Trailer Brakes Connected. Rewiring is sounding more and more likely to be on my plate in the near future, especially if it clears all of this up. 

So, I read that link in the past and I have saved both of them for re-reading later. I will add a couple of notes:

Everyone associated with Chevy GM said "it's the trailer" and everyone NOT associated with Chevy GM said "it's the truck." 

My 'last' auto mechanic was careful to check the ground connection at the bus bar (that was one of the first things he did). It all looked okay to him, and to me (though I don't know much about electrical).

I suspect the wires inside the axles are damaged, having seen the insulation rubbed near the wheels. And my mechanic said he found 'bare copper wire' which didn't make him very happy. 

I'm surprised, given the issues encountered, that OTT hasn't changed the way they approach this brake wiring -- and maybe they have changed it? My trailer is four years old now. 

Thanks to all for the help, links, comments, etc. I will be back. 

Edited 4 hours ago by Boudicca908

[Mike and Carol]

3 hours ago, Boudicca908 said:

I'm surprised, given the issues encountered, that OTT hasn't changed the way they approach this brake wiring -- and maybe they have changed it? My trailer is four years old now. 

My understanding is that the brake wires come that way from Dexter, Oliver just installs the axles as they receive them.  Mike

Edited 1 hour ago by Mike and Carol

[jd1923]

3 hours ago, Boudicca908 said:

Everyone associated with Chevy GM said "it's the trailer" and everyone NOT associated with Chevy GM said "it's the truck."

Knowing for sure is the first step and unfortunately nobody has helped you with this. Service companies often blame the other side to be off the hook, as they charge you an hour for nothing.

If your trailer is the issue, then you wasted time and money with 4 GM dealers. If tested properly, providing certainty "it's the truck" then you would be able to state this fact, not allowing them their BS. The U-Haul idea is a good one, though it seems perhaps you have dismissed the idea. There are other means, but since you are not an electrician it is a simple way for you to know whether your issue is in front of or behind the 7-pin coupler.

BTW, I've known great mechanics that can rebuild engines and transmissions, work perfect brake jobs but no way in the world do they know anything about a 12VDC system other than installing a battery, and you found a dealer that wasn't even capable of doing that!

3 hours ago, Boudicca908 said:

My 'last' auto mechanic was careful to check the ground connection at the bus bar (that was one of the first things he did). It all looked okay to him, and to me (though I don't know much about electrical).

Good ground, so what? Then he quit?

3 hours ago, Boudicca908 said:

I suspect the wires inside the axles are damaged, having seen the insulation rubbed near the wheels. And my mechanic said he found 'bare copper wire' which didn't make him very happy.

"Suspect" is not knowing! If you hire another tech to diagnose your Oliver wiring and this person does not have and use an ammeter, you're again wasting more time and money!

If you are drawing 6A at the two main brake power feeds, then everything downstream is working. You only get a 6A reading if the two magnets on that axle are working, pulling amperage (power from the battery) and properly grounded. If you have frayed wires touch metal, you will not get the constant 6A reading. Instead, it would read zero amps or read way high (live wire touching ground).

It took me all of 5 minutes this morning to grab the ammeter out of my TV toolbox, walk to the edge of our property, pull the pin on the emergency brake, and connect the ammeter to run this test. Maybe the picture below will help in understanding.

Of course, on our Oliver it shows 6A (6.06 actual). I run this test every time I grease the Zerks and do any suspension maintenance. I also check to find 3A at each of the four wheels, so I know the trailer brakes are balanced, working evenly. But for you, if you get 6A on both axles, it shows you do not have a wiring problem below and must be in the trailer harness wiring. If so, it's likely the trailer side of the 7-pin coupler since it takes abuse and weather. The connections interior to the Oliver are less likely, since they are more protected.

I hope you try the U-Haul idea or in some way become CERTAIN in whether your issue is with truck or trailer. If it's the truck, you'e wasting a lot of time and money working on the Oliver, and vice versa. 

The first mechanic you hired should have determined this months ago! Without knowing you will continue to navigate blindly. If it is your Oliver, I hope you finally find a tech that understands trailer braking systems and has some competency in troubleshooting 12VDC systems. Checking a ground is not enough and btw the brake wiring in your pictures all looks pretty good to me.

I'm sorry you have not found qualified help in so many attempts. Although, I understand you believe some of your service techs added value. Bottom-line it's been way too long!

I worked my way through college installing auto alarms, cruise controls, auto-start, keyless entry and high-end stereo systems back in the day (70-80s) when these accessories were all aftermarket additions. It provided me with a solid understanding of automotive 12VDC systems.

I've rewired EVERTHING in our Oliver for mods and to make many corrections where OTT wired things incorrectly. This post repeats a lot of what I wrote last night in my post above. I hope you take some of my advice to heart. In my shop, we'd be done with your issue in a weekend. I hope you take the proper next steps to end this nightmare!

Edited 41 minutes ago by jd1923