Is The Brake Light Relay Needed With The Roadmaster 4 Diode Wiring Harness On 2018 Jeep Wrangler JL?

Updated 05/19/2025 | Published 05/12/2025

Products Featured in This Question

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(372)

$97.92

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

(3187)

$175.28

Roadmaster Stop Light Switch Kit

(623)

$60.78

Roadmaster Brake-Lite Relay Kit for Towed Vehicles

(702)

$47.75

12 Volt Outlet Kit, 20 amps

(331)

$40.45

Question:

When wiring up a 2018 Jeep Wrangler Unlimited JL with a Roadmaster 4 Diode Wiring Harness Part RM-15267 for Flat Towing do I still need the Brake Relay Part RM-88400?

asked by: Charles H

Expert Reply:

Good question, Chuck!

You will not need the Brake Relay # RM-88400 when installing the Roadmaster 4 Diode Wiring Harness # RM-15267 on your 2018 Jeep Wrangler JL Unlimited. This is because the stop light switch circuit on your Jeep JL will go dead while the vehicle is in tow.

With that being said, some of the braking systems will require a stop light switch, like the # RM-751490 (and a 12 volt outlet kit # RM-9332)), but that is dependent on which system it is.

Do you already have a braking system picked out?

expert reply by: Lazer S

Lazer

5/14/2025

I will be using the Blue Ox Patriot portable system

Lazer S.

5/14/2025

@Lazer Nice! That's one of the easiest installs for braking systems and you will not need a stop light switch for it. You will need a 12 Volt Outlet Kit like the # RM-9332 I mentioned though. Your Jeep kills all power after a certain time period when in tow mode so something like this will wire directly to the battery and supply power to the braking system.

Lazer

5/14/2025

@Lazer I already ordered it thanks