You can find the Ford Mustang LED Reverse Light/Rear Fog Light (72-010) here.
Before we get started: The stock wiring colors on this Ford Mustang may differ with your Mustang. Please always use a multi-meter to test your stock wires.
Step 1: Take out the stock reverse light bulb in order to remove the stock reverse lamp assembly.
Step 2: There are two screws located under the bumper that you will need to remove. Once you remove the screws, you'll gain some hand space in the bumper where you can maneuver your hand inside to remove the stock reverse lamp assembly.
To remove the stock reverse lamp assembly, you'll need to remove four screws that secure the stock reverse lamp assembly in place. There are two screws at the top that are somewhat difficult to get to, just be patient when removing the top two screws.
Step 3: Directly install your new Ford Mustang LED rear fog light.
Step 4: Now we are going to move to the trunk to prep for the wiring portion.
There are four knobs located on the edges inside the trunk that you will need to twist off.
Step 5: Remove the trunk liner to expose the firewall hole with a seal in where you will be routing the wires through.
Step 6: Time to wire up your new Ford Mustang LED rear fog light.
This assembly has four wires, but you will only need to draw up three wires up through the firewall hole: black, red, and yellow. You will be leaving the white wire below.
WHITE WIRE: Tap the white wire to the existing reverse light green wire for reverse light function.
BLACK WIRE: Tap black wire to metal ground.
RED WIRE: Tap red wire to driver's side taillight blue wire with purple stripe for taillight function.
YELLOW WIRE: Tap yellow wire to OEM 3rd brake light.
*Note: The yellow wire/brake function is a bit complicated due to the mechanics of the Ford Mustang. The reason why we are tapping the yellow wire to the OEM 3rd brake light is due to the Mustang's unique design of the original taillight that functions as taillight, brake light, and turn signal light. Tapping the yellow wire to the driver's side will result in the LED rear fog light blinking whenever the driver side turn signal is activated. To bypass this, the yellow wire must be routed to the OEM 3rd brake light.
Step 7: Remove the trunk liner to route the yellow wire. There are a few clips holding onto the trunk liner that you'll need to remove as well.
Step 8: Remove the backseat panel, pillar panel, and roof panel so you can route the yellow wire behind.
Step 9: When you open the panels, you will be able to see the existing 3rd brake light yellow wire. Draw the LED rear fog light's yellow wire up behind the panels and tap it to the OEM 3rd brake light (if the yellow wire is not long enough, use similar gauge wires to extend the yellow wires).
Step 10: Close all the panels, put back the trunk liner and all the components.
Step 11: Test to make sure all the functions work and enjoy your new Ford Mustang LED 4th brake light with reverse light, rear fog light, and brake/tail light functions.