Diagram Showing How Trailer Brakes are Wired

Updated 07/16/2025 | Published 09/07/2010

Question:

when you wire tandem axles, do you do it in series or parallel ? how about a diagram ?

asked by: phil

Expert Reply:

The brake wire providing voltage is wired in parallel, with one lead from each magnet being grounded to the trailer frame.

We have a great Wiring Help Page that shows a diagram, I will provide a link to it below.

expert reply by: Mike L

Ed C.

6/30/2025

Just got electric brake setup to replace hydraulics. New backing plate with complete setup shoes, magnets etc. I also got the breakaway switch., new 7 pin cord, and wire for trailer. Now :…. How do I wire the whole thing up? Ed

Mike L.

7/2/2025

@EdC I highly recommend running your trailer's 7-way whip into a junction box like # 3375601100. This provides an organized and clean place to make all your connections so they're protected from the elements. I don't know which whip you have, but be aware that the color coding of the wires in the whip might be different than those of the trailer. Each brake assembly will ground to the trailer frame, with the other wire carrying voltage from the brake controller. Join those into a single lead running to the trailer tongue where you'll install the junction box. The brake output circuit from the vehicle (usually a blue wire) will install on the same junction box terminal as the wire you ran forward from the brakes. I'll link you to a help article that explains this, there are some really nice, easy to understand wiring diagrams that I hope you'll find helpful. I'll also link to an install video for the junction box.

Helpful Links

faq-wiring.aspx

tv-review-buyers-trailer-junction-box-3375601100.aspx

7/2/2025

@MikeL thank you.

Ed C.

7/2/2025

@Ed thanks Mike can you talk to ma about the breakaway box wiring up? How’s that work?