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DIY Trailer Harness for Model Y

Synder

Member
Jun 18, 2021
5
0
Detroit Michigan
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...
 

DayTrippin

Member
Apr 30, 2021
712
680
Jax
Nice work. Definitely helpful for some.

I wasn't 100% sure I would tow with ours but I ordered it anyway. Now it turns out I'll use it a lot sooner than originally planned.

Let us know if you ever get someone at a service center to enable the trailer towing feature in the software. From what I was told, unless you go with the factory hitch, they won't enable it.
 

MikeInFL

Member
May 10, 2014
472
242
Florida
Just tapped into the existing wires on our last Y. (Only did a 4-Pin)
 

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DayTrippin

Member
Apr 30, 2021
712
680
Jax
That is a possibility but at the same time, it could be a liability issue if they do. I think that is where many companies draw the line is if there is some sort of legal liability involved if they do something for you.
 

Webeevdrivers

Active Member
Jan 2, 2017
2,352
4,107
Canada
If someone finds an alternative source for the brake controller pigtail used under the dash when one installs the brake control please let me know. I would like to get my hands on one but Tesla is difficult to deal with on this if you don’t actually have a serial number.

thanks in advance.
 

Synder

Member
Jun 18, 2021
5
0
Detroit Michigan
If someone finds an alternative source for the brake controller pigtail used under the dash when one installs the brake control please let me know. I would like to get my hands on one but Tesla is difficult to deal with on this if you don’t actually have a serial number.

thanks in advance.
You'll see in the pinout of that connector the brake light. Can you use this?
 

52 16 57 39

BioDiesel & Electrons
Nov 20, 2020
260
203
Tacoma, WA
@snyder Clean install. I’m assuming you can move your trailer wiring pigtail around as it looks like there is minimal space for safety chains/drag chains?

I have the stock hitch & wiring, and I am limited in space for my safety chains but wondering if you actually have more space than stock!?
 
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Synder

Member
Jun 18, 2021
5
0
Detroit Michigan
@snyder Clean install. I’m assuming you can move your trailer wiring pigtail around as it looks like there is minimal space for safety chains/drag chains?

I have the stock hitch & wiring, and I am limited in space for my safety chains but wondering if you actually have more space than stock!?
Thanks, towed my first trailer today and there was just enough room to get chains attached albeit rather tight. Getting the locking hitch pin in place was also a little tricky. Worked well overall! You'll also notice that the trailer attached icon is showing. Uncertain if anything else from "trailer mode" was available. Assuming not. Was a very workable solution. No proximity sensors chiming.
 

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a2t2

Member
Jul 8, 2021
282
139
Atlanta
So what was the outcome here? Did plugging into the factory harness without getting a software update cause any issues ? Any proximity sensors chiming ? Can you still us AP while towing ? Thinking of doing the same thing ..
 

Thawk

Member
Jul 6, 2021
47
74
Minnesota
I haven't gone for tow, also had in mind I might hope to add it later - helpful to see, curious about "tow mode" and how important that is (or if there's a way to enable it later)
 

gman99

Member
Dec 9, 2020
9
4
San Diego
@Synder very interested to see this post; excellent information! I stumbled through this myself a short time ago and got it working; it would have been very useful to have your cheat sheet of parts first!


I also see the trailer icon show up but have gone back and forth with Tesla Service to confirm that tow mode is not "enabled" for my vehicle. They were on the edge of turning it on for me but then said that (for now) they would not do so citing possible liability issues. My quip to them is that it's probably a bigger liability to have people attaching hitches and being unable to use tow mode with it...

I've done a few towing weekends (camper trailers) with it and had very positive results. Well worth the addition and still on the lookout for Tesla to sell the proper part (should be 1534249-00-A-003) to swap that in at some point.
 

gman99

Member
Dec 9, 2020
9
4
San Diego
@Synder have you tried out a brake controller yet? I bought this one and it worked great on my first trip with it. Sidesteps the need to send a signal back through the dashboard wiring harness.

 

gman99

Member
Dec 9, 2020
9
4
San Diego
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)
 

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a2t2

Member
Jul 8, 2021
282
139
Atlanta
Was all this above done on a 2020 or a 2021 ? Which VIN ?

Does anyone know if there is some difference between 2020 and 2021 hitch and wiring ?

Uhaul has a nice hitch thats $225 but only lists as 2021. They said it will not fit a 2020...

Regarding the wire harness, I have same question - I wonder if the tesla harness is same 2020 to 2021 ? Im definitely not opposed to just making my own harness per instructions posted above. Sounds easy enough but I do have some questions on the wiring pin out :

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

Is this for 2020? Does someone have a diagram ? White is used twice ?
 

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