My script not working no errors but only the enum material error?

So when I press w or s it does nothing and the enum material code won't work It's in a normal script inside the cars reverse lights mesh Code:

while true do
    ReverseLights = Enum.KeyCode.S
    ReverseLights2 = Enum.KeyCode.W
    if ReverseLights then script.Parent.Transparency = 0 and script.Parent.Material = Enum.Material

    end
    if ReverseLights2 then script.Parent.Transparency = 0.5 and script.Parent.Material = Enum.Material.SmoothPlastic

    end
    script.Parent.Transparency = 0.20
    wait(.20)
    script.Parent.Transparency = 0.20
        wait(.20)
        end