Replacing Blue Wire Missing From 7-Way Wiring Connection

Updated 07/10/2026 | Published 03/23/2022

Products Featured in This Question

Trailer Wiring Junction Box

(827)

$35.23

Curt Echo Wireless Brake Controller - 7-Way Plug-in w/ Bluetooth App - Up to 2 Axles - Proportional

(1918)

$289.95

Question:

I’m missed my blue wire in my seven blade plug pin connector. Do I need a new set of wires or what I can do ?

asked by: Kevin

Expert Reply:

If the 7-way you are referring to is the trailer side connector you will only need the blue wire in the 7-way if your trailer has electric trailer brakes. I do know that there are several trailers on the road with 7-way connectors for the charge line that do not have electric trailer brakes. Very common is small teardrop trailers and popups. If your trailer does have electric brakes then it is best to replace the 7-Way Cord # HM20087 to the Junction Box # 38656.

If you are referring to the vehicle side connector and the only missing wire is the blue wire for the trailer brake controller in your 7-way connector you have options.

You can use a brake controller like the Curt Echo Trailer Brake Controller # C51180 that does not require any input from the blue wire to operate the trailer brakes on up to 2 electric braking axles. It senses brake input from the tail light wires and uses 12 volt power from the auxiliary charge line to operate the brakes.

Otherwise you will need to run a new dedicated wire to the brake controller in your vehicle. If you need help determining exactly what parts you need to do this please let me know what your vehicle and 7-way connection is and I can help you find the correct wiring and additional parts you may need.

expert reply by: Bud M

Vehicle Side 7-Way Connector
(click to enlarge)

Trailer Side 7-Way Connector
(click to enlarge)

Charles C.

7/10/2026

I have an Anderson pull behind 7k and it doesn’t have a blue wire for brakes. I’m putting a new 7way plug on it and can’t figure out what do with black wire and if it goes in blue wire space it’s the only spot for black wire. It worked in the past but not sure how old one was wired!!!!!! Help!!!

Claire H.

7/10/2026

@CharlesC It sounds like you'll need to test the wires for functions. Not all trailer companies use the same standard colors so its possible the black wire is the brake wire. You can use a tester like the # PTW2991 and touch it to the black wire when the brakes are applied. If it detects a pulsing signal, then you'll know that black wire is the brake wire. You can repeat that test with all the wires to confirm the function of each wire to make sure the 7-way is wired up properly.