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Will A Trailers Running Lights Work On Vehicle With 4-Way and Trailer With 7-Way?  

Updated 02/03/2026 | Published 06/30/2024

Question:

Will this kit work for my trailers running lamps? My trailer has a 7 pin plug but i already bought ba 4 on to 7 adaptor.

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Expert Reply:

JD, using the Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # C56281 with a 4 to 7 Adapter # 37185 will allow the running lights, turn signals and brake lights on your 7-way trailer to function. Any reverse lights, trailer brakes or charge line on your trailer will not get power since those are on the other 3 circuits which would have to be hard wired.

expert reply by:
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Bud M
Jesse M. profile picture
Etrailer Expert

Jesse M.

2/3/2026

Hey JD, how did things go with the Curt wiring harness and the 4-to-7 adapter on your trailer? Did the running lights and turn signals work like you needed? Your update could make it easier for the next person setting up a similar connection.

Jd profile picture

Jd

2/3/2026

@JesseM Did not solve the 'no running lights' issue. I had to buy a separate relay & an additional harness in order to tie it in to the main wiring assembly

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