TM3 Trailer Harness Wiring thread.

[cicero1776]

Here is a digital wiring adapter. It plugs into the Tesla trailer connector, so you don’t have to pull any other wires:

"Tesla Model 3 Trailer Digital Wiring Module (Trailer Hitch Lights Connector)"
Tesla Model 3 Trailer Digital Wiring Module (Trailer Hitch Lights Connector) | eBay

I was curious about this module but this link is dead, ebay expires listings after some time. In case anyone else finds their way here, either search ebay with the same title or better yet go to their website at ez-www.com. It's also $50 cheaper there.

I'm not affiliated with it in any way, just trying to save some people time hunting around for it. I did purchase one for my 2021 M3LR. Here's a mini review:

It works as advertised, simply plug it in and you have trailer lights. The major limitation is that it is limited to about 1A (12W) on each of the 3 light circuits. In other words, you need LED trailer lights.

You can't really access to the Tesla side of the plug without taking at least the rear fascia off, but once you have the car apart you can tuck the Tesla plug down behind the bumper. From there you can reach it with the fascia on, through the hatch in the gravel guard. This way is handy if you don't tow things often and want to take the module on and off.

The Tesla side of the plug (3 wire: +/- 12VDC and signal) is a digital signal, presumably connected to the CAN bus on the car upstream. The module converts it to analog and is read-only device, it does not show up on the display or enable 'towing mode' in the software.

 

[cicero1776]

Revisiting this old post because its still the first one to show up on Google. Using the Tekonsha kit previously mentioned. I had lots of success getting things to work first try for minimum effort. KEYWORD: minimal effort. I went to the 12V wire under the rear passenger seat, which lifts away in seconds and immediately presents you with a 12V constant power supply you can wire the box to. Then just route the black lead under the seat, behind the backrest, into the trunk, behind some carpeting, and all the way to the box. Wish more people knew about the 12V under the seat instead of wasting time running a wire through the entire car to the frunk.

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(moderator note - removed sponsored link. if you wish to link the product, re post without it being a sponsored link)

I agree, IMO the penthouse connection under the rear seat is the way to go. Some might argue that in some sort of catastrophic scenario where the HV battery dies, it is safer to connect to the 12V battery, but I figure one would have bigger concerns than trailer lights in such a scenario.

 

[cicero1776]

It's very pricey. It would be nice to know when using this if plugging in trailer lights does the Model 3 screen recognize / show that it knows there is a trailer connected? the ebay listing does not provide this info.

I've purchased one and can tell you it does not, it's a read only device. There is more info on his main site, ez-www.com.

 

[MidlifeCrisis3]

The downside of the Tekonsha is that after you wire it up to the car, you have to power it up and program it. It's a simple process, but if it ever loses power, it forgets its programming and needs re-programming. For me, the Tekonsha forgets its programming every few days. I had a dealer install, and then a replacement dealer install, and I have had this same problem on both units. Both Tekonsha and the dealer have friendly support and are sympathetic, but neither has managed to resolve the issue. Both say they have never encountered "loss of programming" before. Tesla has been extremely unhelpful, and refused to look for any problem that could cause the trailer wiring adapter to lose power. So I'm thinking of the Curt 59236 device mentioned above. Q1 - Does the Curt 59236device continue to work if power is removed? Q2 - Any other comments?

 

[rotarypower101]

Are there any similar alternatives to the expensive Digital Wiring Module utilizing the Tesla 3 pin connector yet?

Recently found out that the Tesla diagnostics software is supposedly capable of changing the tow config variable, allowing the trailer mode switch to be exposed on M3 GUI.

Has anyone accomplished this?

And are there Indy shops in the Portland Oregon area that are capable of changing these config files?

 

[android04]

Are there any similar alternatives to the expensive Digital Wiring Module utilizing the Tesla 3 pin connector yet?

Recently found out that the Tesla diagnostics software is supposedly capable of changing the tow config variable, allowing the trailer mode switch to be exposed on M3 GUI.

Has anyone accomplished this?

And are there Indy shops in the Portland Oregon area that are capable of changing these config files?

The Model 3 does not have official towing capability in North America. I used a Tekonsha tail light converter for towing my trailers for a few years, but it started always lighting up the trailer running lights even when the car was off and asleep because it misread some signal (or lack of signal) in the tail light wiring as "running lights on". Instead of replacing the module, I just connected the trailer light harness directly to my tail light wires and have been using my trailers like that all year. Keep in mind that all my trailers have LED lights. I recommend doing the same and forgetting about any adapters or modules or converters.

 

[rotarypower101]

The Model 3 does not have official towing capability in North America. I used a Tekonsha tail light converter for towing my trailers for a few years, but it started always lighting up the trailer running lights even when the car was off and asleep because it misread some signal (or lack of signal) in the tail light wiring as "running lights on". Instead of replacing the module, I just connected the trailer light harness directly to my tail light wires and have been using my trailers like that all year. Keep in mind that all my trailers have LED lights. I recommend doing the same and forgetting about any adapters or modules or converters.

On the Tekonsha, did you ever have any issues with the device losing settings like one of the users posted about 2 separate Tekonsha devices they tried? Or is that possibly what you are infering with the erratic behavior?

I like that the Tekonsha device is isolated. And possibly able to be tolerant of incandescent bulbs, but it sounds like a half baked solution...

Don't believe I can tap into the existing lights, as I need/want versatility to utilize any trailer despite bulb type, or a trailer wire fouling causing problems back to the towing vehicle if I can avoid those issues.

 

[android04]

On the Tekonsha, did you ever have any issues with the device losing settings like one of the users posted about 2 separate Tekonsha devices they tried? Or is that possibly what you are infering with the erratic behavior?

I like that the Tekonsha device is isolated. And possibly able to be tolerant of incandescent bulbs, but it sounds like a half baked solution...

Don't believe I can tap into the existing lights, as I need/want versatility to utilize any trailer despite bulb type, or a trailer wire fouling causing problems back to the towing vehicle if I can avoid those issues.

I did not get the isolated Tekonsha light converter that has sensors that go around the wires. I used a more conventional kind that you splice to the wires (I believe it was the Tekonsha 119191 ModuLite HD+). This one did not have a learning or programming mode and should just work.