How To Wire In A Camper Shell Third Brake Light On A 2021 GMC Sierra

Updated 08/21/2026 | Published 05/18/2024

Products Featured in This Question

3rd Brake Light Logic Module

(195)

$21.55

14 Gauge Wire - Yellow Primary - Per Foot

(51)

$0.68

Deka Wiring Snap Plug - Male - 16-14 Gauge Wire - PVC Insulation - Blue - Qty 1

(9)

$1.50

Deka Wiring Snap Plug Receptacle - Female - 16-14 Gauge Wire - PVC Insulation - Blue - Qty 1

(6)

$1.21

Hook Probe Circuit Tester

(70)

$13.12

Question:

How do I wire a camper shell 3rd brake light on a 2021 gmc sierra?

asked by: Dan

2021 GMC Sierra With Camper Shell
(click to enlarge)

Expert Reply:

Hey Dan,

To wire in a camper shell third brake light you'll need the 3rd Brake Light Logic Module # PP20-702 you were looking at and you'll need to splice into your Sierra's left and right turn signal functions. You'll need to pop the tail lights out to gain access to the wire harnesses and can then use a tester # PTW2993 to see which wire lights up when the turn signal is on. Once you find both the left and right turn signals you can use a butt connector # DW05744-5 to secure the wiring.

You'll definitely need some extra wire # DW02412-1 to make it from the third brake light to the tail lights and I'd find a somewhat accessible place to splice in some bullet connectors # DW05729-1 (Female) # DW05712-1 (Male) so that you can remove the camper shell without having to pull the tail lights back out to remove the wiring. If you can hide them up under the bedrail that'd be best to avoid anything
hitting them and accidentally knocking them loose.

expert reply by: Kevin C

Wiring Diagram
(click to enlarge)

Dan D.

5/21/2024

Thank you! Folloed these instructions exactly and everything is working perfectly!

Lance H.

8/21/2026

Can you use just one of the turn signal wires?

Lazer S.

8/21/2026

@LanceH That would make it easier, but the module needs to monitor both sides to filter out the blinking signal and ensure the third brake light only illuminates when you press the brake pedal. So it really does need to have both of the yellow wires connected to the turn signals