2015 Golf TDI trailer wiring harness installation

[GolfSW98]

Went to pickup a trailer today and noticed the turn signals don't work. Just remembered the turn signals on my wagen are modified to have the amber bottom signals. Wonder what I have to change on the wiring now

 

[Nuje]

Turn signals on the trailer didn't work?
Here's the layout of the lights (courtesy of @DV52 on other message boards)

I'd take it you're looking for A60 and C31 in the wiring diagrams - that'd be what you need to mate up to the turn signal wires on your trailer wiring harness.

Ok - forget that; don't think that's much help (at least not directly here); this would help if trying to change the coding for any of the lights, so I'll leave it there.

Try this:

M6 is listed as the "left rear turn signal bulb", so black/white wire in position 1 on the OEM connector.

Over on the other side, M8 fits the description - black/green in position 4.

 

[GolfSW98]

Nuje! Big help. I tried to depin the harness until the turn signal stopped then I figured I would move the green interceptor wire over to that pin which would get me turn signals. My depin tool then snapped, just ordered another and will read your post in depth fully and get this sorted. Much appreciated

The more I think about this... may have to go back to original coding on the turn signals. How else will I get brake and turn intercepted on one pin? I would have to get a fancier harness lol

 

[bajaONE]

Thanks for the picture. Couldn’t see the diagram linked earlier, and wasn’t following along on how to do it with just words.

Looking at the connectors as supplied, and as modified, it’s real simple to figure out.
The yellow moves over to the third slot and green moves to the second, from original locations at one side.

Just modified mine, haven’t installed and tested.
Didn’t have a tool to remove the wires and improvised with a little piece of aluminum sheet metal cut real narrow, did the trick. A piece of steel sheet metal would have been better, but it’s not so difficult that soft aluminum can’t work, “tool” shown as well. Photo uploaded to the forum, hope it stays visible for a long time.

finally got the part down here and installed the 118646 on a 2016 tdi variant. did the modification as shown but I have no clue how you could release those pins I had a generic pin removal kit and could not get any to release so soldering gun and shrink wrap to the rescue. so added 20 extra minutes to the install. Just wanted to note here the variant does work with above noted Grigg3 mod for people in the future. Thanks all and Grigg3

 

[GolfSW98]

Ok, so I recoded the tail lights and everything works now. Awesome!

 

[Sleeping_Bag]

Hello! I am to be doing this tomorrow, Thanks for all who put the detailed instructions. I will post pictures of me towing a teardrop next weekend!

 

[Laminated1]

took power from the rear power port

 

[Lug_Nut]

Trailer illumination issues on 2015 GSW w/Tekonsha 118646 .
Followed the yellow and green wire relocation instructions (used a cell phone's SIM tray release tool to release the lock tabs on the pins), and have issues with trailer lights not working correctly, but not the same issue as listed in post 40 of this thread.
Car lamps all off -> trailer lamps all off. Good
Car park lamps on -> trailer side markers and both park lamps (low intensity) both on. Good.
Car left turn on and flashing-> trailer left high intensity flashing. Good.
Car right turn on and flashing-> trailer right high filament flashing. Good.

Here's the issues list
Car brake lamps are on -> trailer side markers and the rear park lamps (low intensity) both on.
Car brake lamps and left turn are on -> trailer marker and park lamps off and right high intensity flashing.
Car brake lamps and right turn are on -> trailer side marker and both park lamps on and left turn high intensity is flashing.
Car brake lamps and park lamps are on -> trailer low intensity lamps are on.
Car brake and park and left turn are on -> all trailer lamps are off.
Car brake and park and right turn are on -> left high intensity flash only.

The trailer lamps used for the input ->output above are all LED. The magnetic base mount tow dolly add-on light I also tried are incandescent and don't react quickly enough to confirm the flashing equivalency absolutely, but the steady (park, brake or both) results are consistent between the trailer LED and the add-on mag base incandescent bulbs.
Power for the Tekonsha was from a regulated 12 volt power supply of 5.8 amp capacity plugged into the house.

Advice or suggestions?

 

[Lug_Nut]

Oh, ...Fer crying out loud....
My car doesn't have LED tail lamps. It has two incandescent bulbs per side. I don't need any special multiplex decode do-dad, just an $8 car flat four connector.

 

[Lug_Nut]

Done. All analogue. No squeeze taps. no splices. No (VW) wire cutting.
Left lamp housing connections:
Combined brake/left turn on black with white stripe wire to trailer yellow wire
Running /marker on grey with black stripe wire to trailer brown wire
Ground on brown wire to trailer white wire
Right housing connection:
Combined brake/right turn on black with green stripe wire to trailer green wire
All trailer wires are soldered on to the stamped metal tracks within the lamp housing.

There are two 21 watt bulbs in my 2015 GSW lamp assembly.
ONE of those two is a low voltage, (duty cycle regulated) park lamp that operates as a brake or turn lamp when at full voltage. This lamp circuit (black with violet on right side, black with red on left) is not used.
The OTHER 21 wall bulb is binary, simply ON, or OFF. It has no halfast triple duty role as a dim tail lamp. THIS is the circuit to use for trailer turn and brake lamp operation.
There is a corner market lamp in the GSW rear lamp assembly, also binary, and this is the circuit to use for trailer tail lamps and clearance markers.

All combinations or lighting functions have been tested and confirmed with our 2023 Alto camper.

Now to repack the Tekonsha for return and refund.

 

[Nuje]

So, you just built a DIY "harness"....?
If you didn't cut, splice, or otherwise tap the existing wires, how did you split them to get their output to the trailer's wiring?

 

[Lug_Nut]

All trailer wires are soldered on to the stamped metal tracks within the lamp housing.

Left side shown
The lower of the two bulbs is lit at full intensity for turn and brake. This is the source for the trailer left and brake.
The upper of the two is lit at half intensity for park, and then at full intensity as an additional turn and brake lamp. This circuit is not used for the trailer.
The 'tabs' to the left of the upper bulb is a 'plug' that fits the mating 'socket' in the lens assembly that powers the side marker lamp unit mounted in the lens. This is the source for the trailer tail lights and side marker lights.
Right side not shown
The right side has only the lower bulb's circuit in use for the trailer right stop/turn. That is the source for the trailer right and brake.

 

[mchapek]

So I just installed a new Curt trailer lights wiring harness into my MKVII 2015 Golf Sportwagon. I'd read all thru this thread and wow, a lot of complicated stuff to get the lights to work. I didn't do ANY of that. I got the Multi-function taillight converter (from torklift central, ordered it when I ordered my eco-hitch). Followed the included install directions, they worked fine. In the end here is how I have the wires from the taillights wired:

Converter box Left turn signal wire goes to the Drivers side black with red stripe wire.
Converter box Right turn signal wire goes to the Passenger side black with green stripe wire (the smaller hatch near the taillight on the passenger side, ran the wire under the plastic trim that goes across the back of the hatch).
Converter box Tail lights signal wire goes to the Drivers side gray with black stripe wire.
Converter box Brake signal wire not used, goes to chassis ground.
Converter box Hot (power) wire goes to the 12 gauge wire I ran from the interior fuse box (could have ran it from the engine compartment fuse box but I ended up running my power-wire inside the car just inside the doors under all the plastic trim, goes up and over the rear tire inside the panel (instead of underneath the car), and my converter box is located inside the Drivers side rear access panel near the taillight).
Converter box Ground wire goes to chassis ground (self tapping screw used, hole near the converter box in the upper right corner of the hatch).
Converter box 4-wire flat trailer-lights-connector follows the Passenger side Turn signal wire from the Drivers side hatch, but instead of running clear across to the Passenger side it drops down thru the metal thru a rounded-ends rectangular hole, and below that is another identical hole that has a plastic plug installed, removed the plug and dropped the connector thru that 2nd hole and outside the car, where it comes down inside the plastic rear bumper trim. Have the connector mounted on a 4-pin flat connector specific L-bracket, which is attached to the underside of the rear-bumper plastic just to the left of the hitch.

Note: I didn't want my converter box to be powered all the time even tho I don't have a trailer attached (as any towing a trailer will be few and far between...don't even have a trailer yet).

So, wanting to be able to turn my trailer lights harness off when I don't have a trailer hooked up (and also know when they are 'ON') my 12 ga power wire runs from inside the fuse box near the driver door to the right under the steering column, and goes to a lighted 12v 30 amp "Trailer light power" switch that I have mounted in a little home-made box that attaches just to the right of the steering-wheel column on the outside of the plastic panel (I made it this way so that in the future it's easily removable, as I didn't want to drill holes in the plastic trim panel that goes from the drivers door to the center console under the steering column).

The wire from the fuse box to the switch is fused for 15amps (came with the harness kit).

The switch has 3 connectors: 1 for incoming power, 1 for outgoing power (load) and 1 that goes to chassis ground which is how the switch 'ON' light works (when the switch is turned ON, the switch light draws a small bit of power off the incoming power, goes thru the switch bulb to light it, and then to ground...the rest of the power goes out the 'load' terminal to power the converter box). And finally, the long length of the power wire runs from the switch 'load' terminal to the converter box 'Power' wire.

All was tested using a 4-pin flat trailer light test unit ($6 on Amazon). The test unit has 3 LED's: Left turn signal, Right turn signal, and Tail-lights.
Here are the testing results (all with the ignition on/engine running):

Left turn signal active, car shows left signal flashing, tester shows left turn LED flashing.
Right turn signal active, car shows right turn signal flashing, tester shows right turn LED flashing.
Tail-lights active (headlights on), car shows both tail-lights active and tester shows Tail-light LED active (tail-lights are dimmer than turn signals).
Brakes activated, car shows both brake lights active, tester shows both left and right turn LED's active (solid on).
Emergency flashers activated, car shows both turn-signal lights flashing together, tester shows both left and right turn Led's flashing together.

And that is that. Now I just need a trailer!

 

[Lug_Nut]

... wow, a lot of complicated stuff to get the lights to work. I didn't do ANY of that. I got the Multi-function taillight converter ....

A big difference in the light-only wiring involved looks to be whether the tail lamps are LED, or are incandescent.
Incandescent car lamp wiring doesn't need the converter. Getting a converter to work correctly with incandescent lamp wiring is near impossible, as I found.
LED car lamp wiring needs a converter to deal with the PWM illumination intensities of the LEDs. Getting the trailer lamps to work correctly with car LEDs, but no converter, is near impossible.
As for 12 volt power (and a separate ground) and the ability to disable that power, I used the 12 volt power outlet already in place in the rear. This high current power is needed with my 7 pin, (electric trailer brakes and emergency breakaway battery maintenance), but is not needed for trailer lighting in my incandescent rear lamp trim level model. My plug in that outlet has an illuminated on-off switch to verify if power is present at the plug. That doesn't mean that any wiring further down in my harness is OK, but if I have trailer brake issues, it makes for an easy halving of suspect wiring.