What Should the Voltage Output Be at the 4-Way Plug on Curt T-Connector Wiring Harness # 56016

Updated 07/07/2025 | Published 04/10/2011

Question:

I recently installed a Curt 56016 powered trailer harness and went to check the 4 pin plug with a voltmeter. It is reading 12 volts on all 3 pins witout the lights even on. I assume I have a bad harness that is somehow shorted out. I was wondering if the the harness should read 12 volts on the black wire only when the the tail lights are on? And then 12 volts flashing in and off for the left and right turn signal. This is how I think it should work logically. I just want to make sure that I have a faulty harness before I send it back. Thank You

asked by: Blake H

Expert Reply:

When you test the 4-Way on the Curt T-Connector Wiring Harness, part # 56016, at the rear of your vehicle, it should show now power on all 3 pins with the lights off. If you have the vehicle head lights on, you should have around 12 volts at the brown (tail lights) pin only. If you apply the brakes, you will have about 12 volts at the green (right turn and brake) and yellow (left turn and brake) pin with the head lights off. If you turn on the right turn signal, you will have around 12 volts flashing at the green pin only and if you turn on the left turn signal you will have around 12 volts flashing at the yellow pin only.

The black power wire should show 12 volts all the time, as long as the fuse in the fuse holder is good.

You will also want to make sure you have the white ground wire on the wiring harness connected to a good, clean ground.

I am including a link to a FAQ page on trailer wiring and it will describe how to troubleshoot your trailer wiring.

expert reply by: Jeff D

Keith

6/11/2025

Would the testing be the same for wiring harness #56395?

Jameson C.

6/11/2025

@Keith Yes it would.

Keith

6/11/2025

@JamesonC - Thank you! Installer is not being very helpful so I decided to get some facts ready. This is what I am getting. The last test of the right turn signal without the car running was just to see if there was a difference (aside from lower voltage without alternator providing higher voltage). Green Yellow Brown Car Off - No lights 0.3 11.9 1.7 Running - Headlights on 0.4 13.5 14.1 Running - Brake pedal pressed 0.4 13.4 3.5 Running - Right Turn Signal 0.3 12.1 2.1 Running - Left Turn Signal 0.4 12.2 2.1 Car Off - Right Signal 0.3 11.6 1.7

Jameson C.

6/11/2025

@Keith Something is definitely goofed up. The green wire should have voltage when brakes and right blinker are on, yellow when brakes and left blinker are on and brown only when running lights.

Dylan J.

7/7/2025

So how many volts should be going to the dome light switch on a reefer unit trailer I’m getting .7 Volts as a reference and the only fuse box that im aware this trailer is is for the reefer unit