What is AX Auxiliary Pin on Hopkins 7-Way Trailer Connector

Updated 11/11/2024 | Published 11/28/2018

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Question:

I want to know the function of a wire called AX, Auxiliary, on a #48505 Hopkins brand 7 blade trailer connection kit for my 2012 GMC Sierra.

asked by: Gerald D

Helpful Expert Reply:

The AX (Auxiliary) location on the Hopkins 48505 connector that you reference, which is the same one used on the Hopkins # H20046, is typically used for 12V power. If you take a circuit tester like part # PTW2979 or # C73NR you should see that the corresponding pin on your 2012 GMC Sierra 7-Way (in the 1 o'clock position) has constant 12V of power running to it.

What you would connect this to on your trailer are things like your batteries, a trailer jack, or anything that would need to be charged or powered when connected to your Sierra.

I have attached a picture of the typical way that a trailer side 7-Way is connected.

expert reply by: Jon G

click to enlarge

Matt

11/8/2024

Hi- related question: same connector as mentioned. When disconnected from towing vehicle the AX light has remained lit, what’s going on here?

Jon G.

11/9/2024

@Matt Does it stay lit permanently, or just for a little bit? And do you have a battery bank on your trailer?

Matt

11/10/2024

@JonG thanks for replying. It’s on permanently and there is an offshore battery onboard.

Jon G.

11/11/2024

@Matt I bet what's happening is your trailer battery is backfeeding and keeping that 12V light lit up. If you install a diode like the Roadmaster # RM-690 it will help to keep this from happening. Before purchasing the diode you can try disconnecting the wiring from your trailer battery to see if that turns the light off or not. If it does, then the diode will be your solution.