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)