What Electrical Components are Needed to Flat Tow a 2021 GMC Sierra 1500

Updated 08/04/2026 | Published 07/26/2026

Products Featured in This Question

Roadmaster 4-Diode Universal Wiring Kit for Towed Vehicles - 7-Way to 6-Way Coiled Adapter Cord

(3605)

$163.34

Blue Ox Patriot Portable Flat Tow Brake System - Proportional

(581)

$1453.03

Question:

What all do I need to install on my GMC 1500 to be able to flat tow electrical wise?

asked by: Toby B

Expert Reply:

Hey Toby, from electrical standpoint there are two main things needed to flat tow a vehicle. There's a braking system and then there's a lighting solution that will be needed.

For lighting you can use the diode kit, # RM-15267, and not have to worry about cutting into the taillight housing. This will splice into your taillight wiring to allow your tow vehicle to control the taillight assemblies of the towed vehicle. This comes with a round 6-way connector that you will install on the front of your towed vehicle and enough coiled wire to go from there to the RV.

The easiest braking system to set up and use is the Blue Ox Patriot # BLU37TR, that applies the vehicle brakes in proportion to how much the tow vehicle is braking. This is the safest way to stop and it reduces wear and tear on both vehicles.

Do you have a base plate kit and tow bar figured out already?

expert reply by: Jameson C

Toby B.

7/30/2026

I have already installed the Blue Ox plate kit. Do I need a battery disconnect?

Jameson C.

7/30/2026

@TobyB Yes a battery disconnect like the part # RM-766 is recommended too as the battery does need to be disconnected before flat towing. Then to power the braking system since the battery will be disconnected you would want the part # RM-9332 as well.

David

7/31/2026

Roadmasters 4 diode is a great safety option to prevent a surge or overload and the braking system. Let it goes training the directions are a little confusing so it took a little time to figure out exactly how to wire the product properly with the help of each trailer tech support and or Roadmaster tech support it was explained correctly so once you understand the process it's an easy install. I've been running the system for two plus years now and have probably over 15,000 miles towing on my toad with no issues whatsoever with the lighting it's highly recommend installing it in your wiring harness.

Jameson C.

8/3/2026

@David great feedback thanks for sharing!

Scott

7/31/2026

Hi Toby I recently installed the Roadmaster 4 diode wiring kit. It took my son and I about 30 minutes to install and has been working flawlessly. It’s a great system that’s discreet and once installed, you don’t ever have to think about it again. You’ll also want a braking system. Some states require you have one. I’ve used the same setup for over 20 years so the initial investment isn’t that bad over the time span you’ll use it. Good luck and have fun

Jameson C.

8/3/2026

@Scott great to hear! What braking system do you have?

Scott

8/3/2026

@JamesonC I’ve been using the old Brake Buddy for well over 20 years. It’s nice that it’s interchangeable as I’ve used it on a few cars, a couple Honda CRV’s and now a Honda Element. It keeps on working, but will upgrade once it finally stops.