How to Wire 4-Pole to 7-Way Adapter and Install Brake Controller on Subaru with 4-Pole Harness

Question:

Hello, I have a 2016 Subaru Outback. I have a 7pin plug mounted but it’s only plugged into a 4 prong adapter. I have all the wireing for the 7 pin but what else do I need to connect it to my controller safely?

asked by: Jayden

Expert Reply:

It looks like your Outback has a 4-pole-to-7-way adapter like # 37185 installed which plugs in to your existing 4-pole wiring to pass along the 4-pole's lighting signals. To activate the additional circuits in the 7-way new wired connections need to be made to support those additional functions.

If you refer to the linked photo of adapter # 37185 you'll see the three pigtail leads provided for making those additional circuit connections for brake controller output, 12V auxiliary trailer power and for trailer reverse lights if needed.

For the brake controller output the blue pigtail on the 7-way adapter needs to connect to the blue output wire on the brake controller. You only need to connect the purple (reverse light) wire if the trailer has reverse lights; otherwise it can be ignored and taped off. For the 12V auxiliary power circuit the black pigtail needs to connect to the vehicle battery + post via a circuit breaker # 9510 using ring terminals # 44-5310A and 10-gauge wire # 10-2-1. The copper post on the breaker connects to the battery. This will use the other wire within # 10-2-1.

You can refer to the linked articles for additional guidance on completing these wiring connections for the 7-way and for the brake controller itself.