Tail Lights Won't Work w/ the Trailer Disconnected from the Hopkins Custom Tail Light Wiring Kit
Updated 09/02/2025 | Published 08/09/2025
Question:
I installed this wiring kit on my 2021 f150. My taillights do not work when I am not connected to the RV. Do I need to connect the original wiring when not towing? Thank you.
asked by: Troy S
Expert Reply:
Hey Troy. Sounds like you have a grounding issue with the Hopkins Custom Tail Light Wiring Kit for Towed Vehicles item # HM77VR. The ground for the wiring harness isn't working and it's causing your lights to only function when you hook up to your trailer and it's ground.
You'll want to make sure your grounding wire is firmly attached to a clean bare piece of metal free of corrosion or paint. Ford uses a lot of aluminum parts in their new trucks so you may want to use a magnet when selecting a grounding location.
What kind of trailer do you have?
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on Flat Tow Wiring Harness
Jerred H.
9/2/2025
Hey Troy, did you manage to fix the grounding issue with your wiring kit? I'm asking to see if this solution worked for you, as it could help others with similar setups.