Toyota Sienna Trailer Wiring | etrailer Trailer Wiring Harness Installation - 2017 Toyota Sienna. Speaker 1: Today on this 2017 Toyota Sienna, we're gonna be having a look at and showing you how to install the Curt T connector vehicle wiring harness with a four pole, flat trailer connector, part number C56261. 2019 Toyota Sienna Trailer Wiring | etrailer Fastest shipping available and a lowest price 2019 Toyota Sienna trailer wiring guarantee. Expert lifetime technical support on all purchases. Complete 2019 Toyota Sienna Trailer Wiring installation instructions and customer reviews. Call 800-298-8924 to place your order or order online at etrailer.com.