Finding the Correct Tail Light Wires on a 2010 Volkswagen GTI to Install Trailer Wiring  

Question:

Expert Reply:

The newer Volkswagen vehicles can be sort of an enigma in terms of trailer wiring. But I will be glad to help you out. There is actually a tech bulletin for this vehicle that I have linked for you and I have included the text below.

Locating the correct wires on the vehicle to hook up a trailer wiring harness. These vehicles have a multiplexed wiring system that sends multiple signals (turn, brake, and tail) along the same wire.

Use only a wiring harness that has a circuit protected battery-powered converter that can detect Pulse Width Modulation (PWM), such as Part # 119250KIT.

First, for the Tail Light and Brake Functions: With a test light, probe the wires behind the vehicles tail light until you locate the wire that contains both the tail and brake functions at 12V. Attach the Red (Stop) wire from 119250KIT unit to wire pointed out below (because there are 2 wires that carry that provide tail light and brake functions).

DO NOT USE the wire where you get pulses of the tail function: (A) Turn - 12V; (B) Brake - 12V; and (C) Tail Light - PWM.

USE: (A) Brake - 12V and (B) Tail Lights - 12V.

Ground the Brown (Tail Light) and White wires from 119190 (as mentioned in the 119190 instructions for the Mercedes; Step 9, 3-wire system, part c).

Next, for Turn Light Functions: Isolated turn signals cannot be found at rear of vehicle, so both the Yellow wire (Left Turn) and Green wire (Right Turn) must be run to the front of the vehicle, along with the Black wire (Battery +). Connections for turn signals must be found at the headlight assemblies.

expert reply by: Michael H

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