What is the Black Wire on the Curt C56403 Taillight Converter for 2019 VW Tiguan For  

Question:

Expert Reply:

The Curt # C56403 is what is referred to as a powered taillight converter. The converter box itself taps into the vehicle's taillight wiring, and converts a 3 wire system (stop lamp, right turn and left turn signal) into a 2 wire system with stop and right turn combined onto one circuit and stop and left turn combined on another.

Older taillight converters also drew the power to run the trailer taillight circuits through each individual circuit itself, but as vehicle wiring systems got more complicated, vehicle manufacturers became more weight conscious in their designs and the price of copper increased, the vehicle's taillight circuits no longer have the excess capacity to supply power to both the vehicle's taillight functions as well as the trailers.

Thus, the powered converter came to be. The connection of the converter to the vehicles taillight circuits is now for switching purposes only. The actual power needed to drive the trailer taillight circuits is drawn directly from the vehicle's battery, which is what the black wire you described is for. This provides for a more reliable connection, higher capacity and also serves to protect the vehicle's taillight circuits from any short circuits that could occur in the trailer's less sophisticated wiring system.

I've linked to an install video for the Curt # C56403 powered converter which is a confirmed fit for your 2019 VW Tiguan. I've also linked to a help article that further explains the process of running the power wire you described to the front of the vehicle where it ultimately connects to the positive battery terminal.

expert reply by: Mike L

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