Troubleshooting LED Trailer Lights Not Working Right When Plugged Into 2020 Mercedes-Benz GLS 450

Updated 07/02/2021 | Published 07/01/2021

Question:

My 2020 GLS 450 was installed with the Stealth hitch with wiring. The trailer LED lights won’t function properly unless the running/headlights are on. Which adapter would you recommend? Is this a common issue with Mercedes? Thank you.

asked by: Byron

Helpful Expert Reply:

It is pretty common for trailer wiring harnesses on Mercedes-Benz vehicles like your 2020 Mercedes-Benz GLS 450 and other German vehicles to have issues with trailers that have LED trailer lights.

The correct adapter to fix this is the 7-Way to 5-Way/4-Way Trailer Adapter for Vehicles with Lamp-Out Sensors Towing Trailers with LEDs # C35FR if your trailer has a 4-way or 5-way flat connector, or the # 20142 if your trailer has a 7-way connector.

These adapters have built in resistors to help your Mercedes detect that a trailer is connected and make sure that it sends power to all of the lighting functions.

expert reply by: Samuel C