4 pin wiring harness to my 7 pin trailer plug Problem

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New member
Nov 30, 2012
My new (to me) Viking PUP trailer has a 7-pin "round" electrical connection including electric brakes.  My vehichle just has the standard 4-pin flat rectangle receiver on its hitch.  I bought an adapter for it but the trailer lights still won't work.  I've double checked both the adapter plugged into my vehicle and the trailer lights both work, but still nothing.  Has anyone had a similar issue?
Don't go farther than the end of the parking lot without a brake controller and proper wiring.

Check the 4-way on your vehicle with a test light (not a meter), and check the ground on the 4-way too.  If it's all good be sure that the connectors on the 4-way are clean and bright.
Your 4-pin flat is not designed to handle brakes.  You would need your vehicle to have a brake controller installed and then a 7-pin connector to allow the brakes to work and for the trailer battery (if it has one) to be charged as you go down the road. 
4 pins are Right turn/stop, left turn/stop, tail/marker and ground (not necessarly in that order) the ground is the "Odd" pin.  Tail next to it and I'm ot sure which turn is which.

7 pin has those 4 plus brakes, battery and "AUX"

You can not adapt from 4 to 7 since the brakes won't work.

You need to upgrade the tow vehicle, adding a brake controller (Teknosha Prodiby?) and a battery charge lead and isolator system.
if the adapter is like mine, check the white wire for continuity...there was none. the white from the round end is designed to attach to the frame.
I am just getting my Curt 4to7 way (57676) installed in my Dakota.  Guy is just doing brakes.  Which wire charges the battery in the trailer? 
On my trailer it is Green=  turn/stop [passenger side]
                          Yellow= turn/stop [drivers side
                          Brown= running lights
                          White=  ground/frame

Seems to be standard, at least on my equipment.

I am just getting my Curt 4to7 way (57676) installed in my Dakota

Perhaps this will help:

Since you are using a 4 pin to 7 pin CONVERTER, like this:


This might help select the correct pin-out:


Looks like it would be the Auxiliary wire connection but you will have to wire it to the appropriate places on both trailer and vehicle. You do not have that wiring now if you have been using a 4 pin plug. There also seems to be some colour confusion between the Aux and Backup light terminals on the Curt charts but I would stick with the Aux pin designation, regardless of colours and wire things up accordingly.
Thanks, I never could remember the other wire colors and plan to add a charging [power] pin to the 6way for my toad..
Now you've made it way easier for me to replace the 7way on my coach w/a 7way/4 flat and cover all towing situations..

Thanks again for those links..

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