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Discussion Starter · #1 · (Edited)
I recently installed a trailer hitch and the required wiring in my 2018 GLA 250.
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I will not repeat details on the installation of the CURT 13197 Class 3 Trailer Hitch, 2-Inch receiver (from Amazon), as the installation procedure is described well in the instructions, and there are plenty of good YouTube videos on how to remove the GLA 250's taillights, and bumper. You will have to temporarily lower the exhaust and the heat shield too. I had to cut a small area out of the bumper to fit back over the hitch. Also, due to concerns about water ingression encountered on the internet, I sealed the area where the metal bumper and the hitch screw back into the GLA. With a good mechanic friend and some tools tools, this should take about two hours. This is all that was needed for a hitch mounted bike rack like the awesome pictured YAKIMA - Ridgeback Tilt-Away Hitch Bike Rack, 4 Bike Capacity (Amazon).

About a year and a half later I decided to tow a Jetski (Waverunner, Personal Water Craft, PWC). I purchased the following accessories (again on Amazon):
  • CURT 59496 Weather-Resistant Powered 3-to-2-Wire Splice-in Trailer Tail Light Converter Kit, 4-Pin Wiring Harness
  • CURT Class 3 Trailer Hitch Ball Mount, Fits 2-Inch Receiver, 1-Inch Hole, 4-In Rise
  • Trailer Ball
  • Trailer Hitch Pin
  • Hitch Tightener
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Discussion Starter · #2 ·
Splicing in the trailer wiring harness was my biggest concern. However, it was the easiest part as it turned out.

The CURT 59496 Powered 3-to-2-Wire Splice-in Trailer Tail Light Converter Kit, 4-Pin Wiring Harness has the following cables:

Vehicle side

GREEN - connect to GLA right turn signal - black and green striped wire

YELLOW - connect to GLA left turn signal - black and yellow striped wire
BROWN - connect to GLA right tail light - black and grey striped wire
RED - connect to GLA right brake light - yellow and white striped wire

WHITE - connect GLA Ground - any metal screw
BLACK - connect to GLA 12V - Black and white striped wire of rear power outlet

I soldered the connections. You may choose the included hardware or wire nuts.
Route the green wire to the right turn signal BEFORE making the connection!
I also included the provided fuse (red) between the power adapter and the black CURT power cable.
Because I will rarely be pulling a trailer, I keep the connector in the trunk, and only take it out when needed. If you do the wiring at the same time as the hitch install, you can attempt to route it through the bumper. You may need additional parts for that, and drilling may be required.

Here are pictures of the wiring:

CURT 59496 Powered 3-to-2-Wire Splice-in Trailer Tail Light Converter Kit, 4-Pin Wiring Harness
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Routing the green wire (step 1)
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Routing the green wire (step 2)
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Connecting the green wire to the right light (step 3)
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Hiding the green wire (step 4)
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Yellow, red and brown wire connection to the left light
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Ground wire
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12V wire with fuse. Power supply can be seen in the upper right.
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All tucked in. See the power supply again in the upper right.
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This works for me. You may like to route the cable through or below the bumper for a permanent setting.
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