How do I detect which direction a part is moving, relative to its local axis?

Lately, I have made a simple vehicle with lights, and I am trying to add reverse lights to it, but I only would like them to activate when the VehicleSeat is moving backwards (relative to Back face). I believe this might use CFrame, but I currently have no idea how to do this.

Here's the script for the motors and lights I currently have. I just need to know how to detect if the seat is moving backwards on its local Z-axis, so I can combine that with the Throttle detection.

seat = script.Parent
wheels = script.Parent.Parent
frontleft = wheels.FrontLeft.Motor
frontright = wheels.FrontRight.Motor
rearleft = wheels.RearLeft.Motor
rearright = wheels.RearRight.Motor
left = wheels.LeftSteer.Steer
right = wheels.RightSteer.Steer
body = wheels.Parent.Body

while true do
    wait()
    if seat.Throttle > 0 then
        frontleft.AngularVelocity = 60
        frontright.AngularVelocity = -60
        rearleft.AngularVelocity = 60
        rearright.AngularVelocity = -60
        body.BrakeL.Material = Enum.Material.SmoothPlastic
        body.BrakeM.Material = Enum.Material.SmoothPlastic
        body.BrakeR.Material = Enum.Material.SmoothPlastic
        body.BrakeL.PointLight.Enabled = false
        body.BrakeM.PointLight.Enabled = false
        body.BrakeR.PointLight.Enabled = false
    end
    if seat.Throttle == 0 then
        frontleft.AngularVelocity = 0
        frontright.AngularVelocity = 0
        rearleft.AngularVelocity = 0
        rearright.AngularVelocity = 0
    end
    if seat.Throttle < 0 then
        frontleft.AngularVelocity = -60
        frontright.AngularVelocity = 60
        rearleft.AngularVelocity = -60
        rearright.AngularVelocity = 60
        body.BrakeL.Material = Enum.Material.Neon
        body.BrakeM.Material = Enum.Material.Neon
        body.BrakeR.Material = Enum.Material.Neon
        body.BrakeL.PointLight.Enabled = true
        body.BrakeM.PointLight.Enabled = true
        body.BrakeR.PointLight.Enabled = true
    end
    if seat.Steer > 0 then
        left.TargetAngle = 30
        right.TargetAngle = 30
        left.AngularSpeed = 5
        right.AngularSpeed = 5
    end
    if seat.Steer == 0 then
        left.TargetAngle = 0
        right.TargetAngle = 0
        left.AngularSpeed = 5
        right.AngularSpeed = 5
    end
    if seat.Steer < 0 then
        left.TargetAngle = -30
        right.TargetAngle = -30
        left.AngularSpeed = 5
        right.AngularSpeed = 5
    end
end

Also just an off-topic note, IDK if this is happening on your computers too or just mine, but the advertisement for "Community Chat" is blocking out buttons, disallowing me to post questions, or write them (had to use Ctrl-MouseWheel to access "Ask Question" button)