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Discussion Starter · #1 ·
Here is a solution for anyone wanting to install trailer wiring. My Pro S was delivered as "Vehicles without trailer preparation", which means that if I wanted to install the VW OEM wiring kit I would need to run a wiring harness to the front of the vehicle and mess with CANbus wiring under the dash. The solution below is much easier to install, but be aware it will not allow coding to auto-adjust stability control, steer assist, etc.
I purchased a Tekonsha 119250 Trailer wiring module. It requires no direct contact with the wires in the car as it uses split-core hall effect current sensors. It works perfectly for me.
Since there is no cutting or splicing this should not void the warranty, and it's not adding any load to the wires, so does not create error codes.
Detailed instructions for the ID.4 Pro S:
Remove the two lower plastic tracks. Three T30 Torx screws at the bottom.
Remove the floorboard.
Remove the scuff plate trim piece by pulling it straight up (clips only, no fasteners).
Remove the one T25 Torx screw inside the cover hinge hole, on both sides. For this kit you will need access to both side panels.
Hood Automotive tire Vehicle Steering wheel Steering part

The side panels can now be pulled back (three metal clips). It can be gently pried back to allow enough access without removing completely.
Unplug the connectors from the power outlet and interior lights to avoid strain on the cables.
White Product Automotive design Hood Automotive tire

Find the wiring bundle that goes into the rear corner lights.
The left side has three wires (Brown, Black/Gray, Black/Red), wrapped in foam-cloth tape. Remove the tape to access the wires.
Light Gadget Electrical wiring Line Circuit component

Black/Gray is the tail light. Attach sensor with Brown sticker.
Black/Red is Left Turn and Brake. Attach sensor with Yellow sticker.
Automotive design Hood Motor vehicle Automotive lighting Headgear

White Motor vehicle Automotive design Hood Automotive tire

The Right side has four wires (Brown, Black/Purple, 2 x Gray/Red), wrapped in foam-cloth tape. Remove the tape to access the wires.
Black/Purple is Right Turn and Brake. Attach sensor with Green sticker.
The wire going to the right side can be conveniently taped with cloth friction tape to mount points for the liftgate sensor wire (under the scuff plate trim).
Sensor with Red sticker is not used and should be secured.
Important: When attaching the sensors make sure the arrow (clip end) is closest/pointing to the lights.
Motor vehicle Hood Automotive design Trunk Electrical wiring

There are two convenient grounding points on the left side of the car. I used one to mount the module and the other for the ground wire.
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I took power from the 12V "cigarette" outlet in the rear, via a 15A fuse. I made a pigtail jumper/adapter so that no wires need to be cut. These are the plug (1J0919321) and terminals (N90696603) used on the power outlet connector. Another alternative would be to simply run the power wire into a "cigarette" plug, and only plug it in when towing a trailer.
The Tekonsha kit includes some adhesive foam sheets to wrap the sensors. I also wrapped the wires in cloth friction tape from the local hardware store, to prevent rattles and wire chafing.
The module does some calibration on initial power-up, so sometimes it takes a minute to get its act together, but after that it works as expected. The module is supposed to be powered permanently (which can be accomplished by changing Fuse 52 position), but I prefer that it powers down when the car is off.
Automotive tire Automotive lighting Hood Motor vehicle Automotive design

On the left side remove the plastic plug. Feed the 4 pin trailer plug through a new rubber grommet ( 1.75" drill hole size). Insert the rubber grommet.
 

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2021 ID.4 RWD Pro S w/Gradient, 2022 Mini Cooper SE, former: 2015 Tesla Model S 70D, 2013 Volt
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Fantastic write up.
 

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2021 ID.4 RWD Pro S w/Gradient, 2022 Mini Cooper SE, former: 2015 Tesla Model S 70D, 2013 Volt
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55 Posts
Where did you end up running the wire to exit the car?
 

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Discussion Starter · #4 ·

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2021 ID.4 RWD Pro S w/Gradient, 2022 Mini Cooper SE, former: 2015 Tesla Model S 70D, 2013 Volt
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There is a plastic cap/grommet covering a 45mm hole right where the red arrow is, below. You could try cutting a hole in the plastic grommet. I replaced it with one of these rubber ones:
View attachment 5713
Did you then have to pull the bumper to get it through the hitch cut out? Trying to avoid removing my bumper again.
 

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Discussion Starter · #6 ·
You should be able to fish it through without removing the bumper. You can actually see the plastic grommet if you look through the gap in the plastic trim where the left rear tow eye is (the grommet is directly behind the left rear wheel). Here is a picture I just took looking through that gap.
Automotive lighting Vehicle door Gas Tints and shades Fixture
 

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2021 ID.4 RWD Pro S w/Gradient, 2022 Mini Cooper SE, former: 2015 Tesla Model S 70D, 2013 Volt
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You should be able to fish it through without removing the bumper. You can actually see the plastic grommet if you look through the gap in the plastic trim where the left rear tow eye is (the grommet is directly behind the left rear wheel). Here is a picture I just took looking through that gap.
View attachment 5714
Is it one of these holes? (But on driver side)
Engineering Machine Auto part Space Automotive design
 

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Discussion Starter · #8 ·
Yes, that's it. It will be obvious when you have the side panel peeled back :)
 

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2021 ID.4 RWD Pro S w/Gradient, 2022 Mini Cooper SE, former: 2015 Tesla Model S 70D, 2013 Volt
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Yes, that's it. It will be obvious when you have the side panel peeled back :)
Ordered the grommets and Tekonsha kit! I’ll probably make a video about this as well and link to your guide. Glad to not be the first doing it. Do you know if the tail lights are run by PWM?
 

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Discussion Starter · #10 ·
I am not sure if it's PWM. There are no exposed wires or plugs back there to attach a voltmeter or oscilloscope.
A video would be good, it was my initial plan, but trying to take video in the confined space was cumbersome, so I gave up in favor of stills.
 
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