DIY Trailer Harness for Model Y

[NaperY]

I'm always a bit nervous about 3rd party supplied connectors, plus multiplying it over an extra 4 times. I'd much rather splice and solder the cables, then i know if i have light(s) out on the trailer that it 100% is the trailer lighting and not the car's.

 

[NaperY]

Any information? Because, I am in the same situation.

I found an update in a service bulletin. I'm guessing because of the chip shortage, Tesla installed different body modules in 2021/22 MY with tow package than without. The service bulletin says that if folks opt for the post-delivery tow hitch installation that the LH Body Controller module would also need to be replaced.
just a hunch, but makes sense why the rear trailer light harness is dead.

 

[gluz24]

One more share... this is how I gained back some clearance under the bumper for the chains vs. jamming the connector in that same recess. (hitch extender rated to 3500lbs)

Hi, I am planning on doing similar. Can you share where you got the 2 inch clamp for 7 pin? Thank you

 

[schmiddj]

Trying to get this excellent thread revived - has anyone tried this on a 2022 MY? I'm about to give it a try and wondering if there's any experience/differences noted with the 2022 model, which seems to have changed a few things (I have the 15V Li-ion battery). Just installed the Draw-Tite 76430 hitch and the ZCI zero contact trailer wiring kit as a placeholder, but I eventually need trailer brake support.

 

[schmiddj]

Trying to get this excellent thread revived - has anyone tried this on a 2022 MY? I'm about to give it a try and wondering if there's any experience/differences noted with the 2022 model, which seems to have changed a few things (I have the 15V Li-ion battery). Just installed the Draw-Tite 76430 hitch and the ZCI zero contact trailer wiring kit as a placeholder, but I eventually need trailer brake support.

Whoops - "revive" probably wasn't the right term; the forum was hiding the most recent posts from me. Gonna try out

Trying to get this excellent thread revived - has anyone tried this on a 2022 MY? I'm about to give it a try and wondering if there's any experience/differences noted with the 2022 model, which seems to have changed a few things (I have the 15V Li-ion battery). Just installed the Draw-Tite 76430 hitch and the ZCI zero contact trailer wiring kit as a placeholder, but I eventually need trailer brake support.

Whoops - "revive" probably wasn't the right term; the forum was hiding the most recent posts from me. Gonna try out cFelix's wiring, as I suspect my 2022 MY is similar. We'll see if it works.

 

[schmiddj]

Whoops - "revive" probably wasn't the right term; the forum was hiding the most recent posts from me. Gonna try out cFelix's wiring, as I suspect my 2022 MY is similar. We'll see if it works.

Nevermind. Can confirm - the stock trailer wiring molex plug is completely dead in 2022 Model Ys that shipped without the tow package. No voltage on any connectors - the only wires that are connected are the grounds (two black corner connectors). Guess I'll have to live with a 4-pin trailer plug and inertia-based trailer brakes. Thanks NaperY for the service bulletin info - I should've listened.

 

[iceblade]

I purchased a Model Y Performance in June of last year and opted ot not have the trailer package installed. A year later I've come to realize how useful it would be to tow a trailer with my Y, so I spent some time scraping this site and others on guidance in building a trailering harness that uses the OEM connector under the bumper cover. While for sure you can go buy a Curt harness kit and clip it to your lights, run power etc... I wanted a cleaner solution.

Kudos to gman99 who got me started down the right path on finding a connector that will fit on the existing trailer harness connector installed on all(?) Model Y's.

To build the connector you will need:
- 1X Molex Connector (Male) Part Number: 34986-1601
- 7X Molex Automotive Connector Pins (Male) Part Number: 31296-0008
- Some Molex automotive crimping tool
- 16 gauge wire

Here are the application notes from Molex explaining assembly of the connector: https://www.molex.com/pdm_docs/as/AS-33472-100-001.pdf

And the pinout for the tesla connector is:

- Black (corner): Unknown
- White: Ground
- Not Used
- Red: Brake Lights
- Blue: Unknown
- Not Used
- Not Used
- Red (corner): 13V Supply
- Purple (corner): Unknown
- Black: Unknown
- Not Used
- White: Reverse Lights
- Brown: Running Lights
- Purple: Passenger's Blinker
- Green: Driver's Blinker
- Blue (corner): Unknown

The pinout for a standard 4 or 7 pin trailer hitch is easy to get from google or whatever connector you end up buying. I went with this: https://www.amazon.com/gp/product/B07YZ16N5D/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Slap together both connectors (male tesla connector + 7 or 4 pin universal trailer harness) and you have a working Trailer harness. Note that this likely will have limited functionality - and of course choose your gauge carefully based on the requirements of your trailer lighting. Choosing incorrectly may result in fire or something like a dead tesla...

Thanks for this wonderful post. I got my 7pin trailer harness made. On my testing I can't get +12V on the Brown: Running Lights. Are they only energized when set to Drive

Just wanted to chime in. I bought the harness for my model y and installed a week ago. While it plugs in just fine, im not receiving any voltage on break/turn signal. I contacted them for support so we'll see what's up.

Thanks @snyder for the extensive write-up. I made my own harness cable. I get Left/Right pin to power up when the car is not in park mode. The "running light is not working. The moment I switch to "D" mode. Everything stop working. So I'm wondering if this is the same issue you're seeing?

 

[iceblade]

I purchased a Model Y Performance in June of last year and opted ot not have the trailer package installed. A year later I've come to realize how useful it would be to tow a trailer with my Y, so I spent some time scraping this site and others on guidance in building a trailering harness that uses the OEM connector under the bumper cover. While for sure you can go buy a Curt harness kit and clip it to your lights, run power etc... I wanted a cleaner solution.

Kudos to gman99 who got me started down the right path on finding a connector that will fit on the existing trailer harness connector installed on all(?) Model Y's.

To build the connector you will need:
- 1X Molex Connector (Male) Part Number: 34986-1601
- 7X Molex Automotive Connector Pins (Male) Part Number: 31296-0008
- Some Molex automotive crimping tool
- 16 gauge wire

Here are the application notes from Molex explaining assembly of the connector: https://www.molex.com/pdm_docs/as/AS-33472-100-001.pdf

And the pinout for the tesla connector is:

- Black (corner): Unknown
- White: Ground
- Not Used
- Red: Brake Lights
- Blue: Unknown
- Not Used
- Not Used
- Red (corner): 13V Supply
- Purple (corner): Unknown
- Black: Unknown
- Not Used
- White: Reverse Lights
- Brown: Running Lights
- Purple: Passenger's Blinker
- Green: Driver's Blinker
- Blue (corner): Unknown

The pinout for a standard 4 or 7 pin trailer hitch is easy to get from google or whatever connector you end up buying. I went with this: https://www.amazon.com/gp/product/B07YZ16N5D/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Slap together both connectors (male tesla connector + 7 or 4 pin universal trailer harness) and you have a working Trailer harness. Note that this likely will have limited functionality - and of course choose your gauge carefully based on the requirements of your trailer lighting. Choosing incorrectly may result in fire or something like a dead tesla...

I found this ebay item selling the Tesla OEM wiring harness (attached photos). Looking at the pinout, looks like it's using 3 corners of the molex to tap into 12V, Brake and Running Lights. Looks like Red, Purple and Blue wires. Any idea what they are?

 

[NoHoCody]

Good thing I came by here; so I got a (TESLA) OEM trailer hitch from some guy here in LA, is brand new and comes with the wiring harness direct fit; I'll post pictures later if i can; I will install sometime this week; is good to know that my lights will work without trailer mode available...

You never posted the pictures and what was the result. Lol, I'm doing the same thing now from someone in LA also

 

[Ned@DriveEV]

I have a theory, but no ewasy way to prove it... keen to hear if anyone has any more ideas.

It seems like the eary cars had the lights enabled on the factory loom, right? Guessing those are the old Lead Acid 12V models? Can anyoen check body control modul part number on your car by any chance? we didnt get any of them here until late 2022, so all lithium.

Then it seems they had a 12V output issue with the trailer wiring due to the new lithium batteries. Some people talking about the 12V not being available when they first got the car, and then got the body control module replaced and the 12V output worked?

So im thinking they disabled the outputs and they come live when tow mode is enabled, and that the lights should comne active without a control module swap, but no 12V for the trailer?

Can anyone confirm any of those theories? or shed some more light into it?

 

[Herbie65]

There seems to be 3 ECU versions the first 2 are clear one has NO TOW, the other has TOW, but mine is the premium. Does this one have tow mode or not?

 

[MYLR_ON_CA]

Thank you OP for the Molex part number, if I want to build the OEM harness for an OEM hitch I buy from EBay (without harness). Is there a known part number of the other end of the connector that goes in the socket on the hitch? It’s round connector.