Why Can't You Use Trailer Wiring for Stoplight Circuit for Brake Controller

Published 09/11/2024

Question:

Hey Evangeline, I'm looking into this for my 2023 Forester. Is there a reason why the 4-pin wiring harness brake signal can't be used with this diode and it has to be the CMHSL? From my understanding, all the brake signals light up with adaptive cruise, but I may be wrong. Thanks! Josh

asked by: Josh

Expert Reply:

Hey Josh, so the reason you can't use the brake light signal from a 4-way trailer wiring harness for the stoplight circuit of a brake controller like the Redarc Tow Pro Elite part # RED44FR is because this circuit also has the blinker circuit so the brake controller would try to activate with every flash of the blinker.

This is why you need a dedicated brake light circuit which is available at the brake switch.

expert reply by: Jameson C