startup.lua

modem = peripheral.wrap("left")

redstone.setOutput("top", false)

while true do
    event, modemSide, senderChannel, replyChannel, message, senderDistance = os.pullEvent("modem_message")

    if message == "on" then
        redstone.setOutput("top", true)
    end

    if message == "off" then
        redstone.setOutput("top", false)
    end
end