How to Determine Which Wire is Ground and Which Wire is 12V Power for a 7-Way Connector

Updated 06/28/2017 | Published 06/27/2017

Question:

I have a seven pin vehicle-side connector for my trailer that needed to be replaced due to corrosion. I have all the lights working but the brakes do not. I believe that the blue wire is for the brakes but there are two black wires, one that is fed along side the blue brake wire and a separate black wire that is grounded to the vehicle. Which black wire is for the 12-volt connection?

asked by: Dave

Expert Reply:

Since your 12V Power is run from the battery to the 7-Way connector, the black wire that is grounded to the vehicle will definitely not be the 12V Power wire.

My bet would be that the other black wire that is run alongside the blue wire for your brake controller is the correct wire. You will want to test it with a Circuit Tester # PTW2992 first though to make sure that this is correct since not all wiring is the same color on vehicles and trailers.

The 12V Power will need to be connected to the pin in the 1 o'clock position on your 7-Way and the Ground will need to be connected to the pin in the 7 o'clock position.

I have attached a picture and a helpful article for you to check out as well.

expert reply by: Jon G