Model 3 trailer loom wiring

[NMZooming]

I thought people might appreciate an easier way to tap unswitched power for the Tekonsha no. 119250 adapter and products like it. I noticed that some members suggest tapping into the gray, three-prong plug under the rear bumper cover with switched power, that is available in 2019 Model 3s and later.

eTrailer, where I bought my Stealth EcoHitch, and others suggest running a wire all the way to the Frunk, to attach it to the 12V battery's positive cable terminal.

However, after connecting the Tekonsha adapter to the taillights, here is a much shorter routing inside the vehicle:

1) remove the rear seat bottom cushion - just feel under the front edge for two tabs and slide them toward the left-hand side to lift the front edge, pull the cushion forward and up to disengage the seat belt buckles, and unclip the bum warmers;

2) remove the foam cover on the right-hand side to reveal the end of the battery cable - see photos;

3) Fully lower the windows to avoid being locked out inadvertently;

4) On the touchscreen, touch Controls > Safety & Security > Vehicle Power > Power Off;

5) remove the trim piece next to the right-hand seat back and run an AWG # 12 wire from the Tekonsha's power (positive) lead from the trunk (behind the right side trim panels) through a grommet into the area under the seat to the end of the battery cable shown in the pictures;

6) remove the negative ground strap and wrap it in a rag to prevent it from grounding;

7) remove the nut on the positive end of the cable (see pictures) and attach a connector crimped onto the AWG # 12 wire from the Tekonsha's power lead, then replace the nut and the ground strap.

Replace everything, power the vehicle back on, and run through the Tekonsha's 'learning' protocol.

 

[NMZooming]

Update: I was wrong, and it's even easier re: step # 5, as there's no need to find a grommet. The loom runs past a chunk of foam Tesla has stuffed up behind the trim panel in the passage from the trunk leading forward ahead of the subwoofer. You just pull out the foam, noting its orientation, and once the trim piece next to the right-hand seat back is out, you lean down the seat back and it's easy to feed the AWG # 12 wire through. I zip-tied my power wire to the loom every 6" or so and it came out fine.

Also: you don't really have to remove the ground strap shown in the photos. Just be careful not to ground the connector while slipping it onto the positive post until the nut is back in place holding everything together.

Finally: there is an unused grommet--which Tesla painted white--below the right-hand taillight that is perfect for passing the trailer plug pigtail through. Of course, you have to cut and solder the 4-wire pigtail back together, but no biggie. The result is very tidy, and you're not shutting the trunk onto the pigtail over and over.

I ended up buying a good used diffuser with the square removable door, and will post mine on eBay for someone who doesn't have a hitch. I didn't want to cut an oval hole and use that clunky magnet affair that e-Trailer sells.

 

[NMZooming]

Here are some images of the finished result. The car pulls the utility trailer far better than the Subaru did. Power drain is considerable, and I'm going to move the spare to the side so it's edge-on for aerodynamics rather than the way it's oriented now. The ability to have a bike/ski rack that doesn't involve the glass roof is very nice.

 

[Scurry]

Wish THIS was the first google result for this topic instead of that other thread

 

[phomazing]

The manufacturer of this wiring kit advise against running the wire to an existing 12v outlet for the risk that you take overloading the circuit. If you over load the factory fuse, you will blow it. You would then lose all lighting functions on your trailer. Running the power wire directly to the battery will allow it to have its own fuse and most optimal power source. https://www.etrailer.com/Trailer-Wiring/Tekonsha/119250KIT.html

I got the Curt Taillight Converter 59236 and ended up routing the power to power under the rear seats like you suggested. I hope it works when I get my trailer later this week.

Question on your setup though. according to the quoted above from the YouTube video, was wondering if you had any issues with your setup so far? has all been good?

 

[android04]

I got the Curt Taillight Converter 59236 and ended up routing the power to power under the rear seats like you suggested. I hope it works when I get my trailer later this week.

Question on your setup though. according to the quoted above from the YouTube video, was wondering if you had any issues with your setup so far? has all been good?

There will be no issues with drawing power from the 12v output under the rear seat. Your wiring kit should include a fuse that you will install inches away from the bolt outputting the 12v under the seat, and that will protect the 12v system from any short circuits or large power draws that come from your trailer light adapter wiring. Also, you will not overload that 12v output under the seat by running trailer lights from it. That 12v source powers ALL 12v devices on the car and charges the 12v battery. Trailer lights are nothing to it because it can output about 180 Amps.