Trailer lights problem

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W WA
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2020 CX-5 GT
I think it’s unlikely that my Mazda is responsible for this problem, but throwing this out there hoping someone can steer me in the right direction.

I have a 2020 CX5 GT. About a week ago I had a class 3 hitch and wiring installed at UHaul. Later that day I picked up a new utility trailer, checked the lights before driving home and everything was working correctly. A few days later I hooked up the lights again and they did not work, no turn signals, no brake lights, and the running lights were on (but dim) even when the ignition was off. I went back to UHaul, they replaced all the wiring, and the lights worked correctly again. I hooked up the trailer and lights again today for a 500 mile drive. Lights were working fine. Now at a hotel and I notice the running lights are on again with the ignition off. The left turn signal works but right one does not. Similar but slightly different than the first failure.

Its hard to imagine that 2 wiring harnesses were defective and failed like this. I wonder if there could be an intermittent short in the wiring on the trailer itself that blows out the controller module? As I said, it’s a brand new trailer. All the lighting is low current LEDs.

Any ideas?
 
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2006 Mazda5
For what it is worth, when I wired mine, the first converter was acting exactly like your failures. My second converter has been working for 6 months now. Maybe there is a bad batch of converters. I don’t remember the brand of mine off the top of my head.
 
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W WA
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2020 CX-5 GT
Was it a Curt @mmssow ? I stopped at a U Haul place in Boise this morning and they suggested trying Tekonsha wiring, said it was more robust than the Curt Product.

They also said the problem could be with my aluminum trailer, saying they are problematic for trailer wiring but I’m skeptical of this.
 
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2006 Mazda5
Was it a Curt @mmssow ? I stopped at a U Haul place in Boise this morning and they suggested trying Tekonsha wiring, said it was more robust than the Curt Product.

They also said the problem could be with my aluminum trailer, saying they are problematic for trailer wiring but I’m skeptical of this.

I can’t say for certain it was a Curt. I don’t remember and it’s hidden now, since it is installed. It is likely though it was a Curt because I tend to buy a lot of Curt branded hitches and wiring over other brands.
 
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2018 AWD GT Premium Red/Black
I used the Canadian harness and installed it myself. It's the only one I'm aware of that doesn't require piercing of any insulation, nor running power 12V directly from the battery.

It's completely reversible, assuming I can back the power pin out of the existing light harness it snapped into.
 
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Mazda Protege DX
I used the Canadian harness and installed it myself. It's the only one I'm aware of that doesn't require piercing of any insulation, nor running power 12V directly from the battery.

It's completely reversible, assuming I can back the power pin out of the existing light harness it snapped into.
Depinning it is such a b****, you need a pin tool for sure. I tried to transfer my hitch harness from my 19 to 20, end up cutting the wire and tapping into the other harness directly.
 
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2018 AWD GT Premium Red/Black
Depinning it is such a b****, you need a pin tool for sure. I tried to transfer my hitch harness from my 19 to 20, end up cutting the wire and tapping into the other harness directly.
They aren't that expensive. I mentioned the reversibility more to point out that it seems low risk of harming the car, and if it did cause problems it could be extracted without any lasting change to the car. I really don't like the idea of tapping into wiring by piercing insulation. That really rubs me the wrong way.

Also wasn't thrilled at the prospect of running a wire kludged into the engine compartment on the far end of the car, and then hiding its path to the rear.
 
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2019 CX-5 Signature
I used the Canadian harness and installed it myself. It's the only one I'm aware of that doesn't require piercing of any insulation, nor running power 12V directly from the battery.

It's completely reversible, assuming I can back the power pin out of the existing light harness it snapped into.
Funny. I purchased the Canadian trailer harness and never installed it. What’s this pin reversal? I realized I never had the proper install method. I assumed it was just a y harness and plug and play.
 
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Mazda Protege DX
It is essentially plug and play, it’s good because it's oem and it’s designed for the car and not some universal s***, it comes with body plug and such, the harness has a control module and it needs power which you install this pin into a existing connector on the car.
 
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W WA
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2020 CX-5 GT
After having the two Curt wiring harnesses fail I installed a Teknosha harness yesterday (part #118746). It is supposedly more robust than the Curt harness.

One thing I did different on the install was to run the ground to an existing ground point. The U-Haul tech that installed the Curt harnesses drilled a hole in the sheet metal around the hatch opening and used a self-tapping screw to secure the ground wire. It appeared to be a solid ground, I put an ohm-meter on it and tested it, but maybe it was intermittent of insufficient in some way. Using the existing ground point with 10mm bolt seemed like a better way to go.

Before installing the new harness I had the trailer wiring checked out by the company where I purchased it and they could find nothing wrong with the wiring.

I don't have any long tows coming up so not sure when I will have a definitive evaluation of the new harness. It works fine after installation but so did the two Curt harnesses.
 

Buzzard

2016 Cx-5 GT
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Mazda CX-5 GT
If I'd have seen a "tech" drill a hole for a self-tapping screw, he'd have had a .40S&W screwed into his ear. Depending upon your location, he just invited corrosion to your world.
 
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W WA
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2020 CX-5 GT
If I'd have seen a "tech" drill a hole for a self-tapping screw, he'd have had a .40S&W screwed into his ear. Depending upon your location, he just invited corrosion to your world.
The hole is in interior sheet metal, not exposed to weather, so I'm not very worried about it.
 
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2018 CX-5 Sport
I found my eBay order. It was a Curt 56377 harness.
I have the same Curt harness. I only used my trailer twice so I don't know if it is a bad one or not, the two times it worked fine. I tried to find the wire terminal that the Canadian harness has, so I could get power from the rear terminal block like the Canadian harness does, but I couldn't find it.
 
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2018 CX-5 Sport
When I got my Curt harness, the black control box did not have any label or markings on it so I called Curt. They said yes, that is a genuine Curt part.
 
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W WA
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2020 CX-5 GT
The new Tekonsha harness appears to be working just fine, I made a 400 trip pulling the trailer this week and lights still worked when I returned. That's more than I can say about the 2 Curt harnesses I had.
 
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