first program in c#

[bkruep]

I am trying to pick up c# and was wondering if someone could show me what I am doing wrong. In the code below I have three radio buttons(go, slow down, and stop). I also have a checkbox is show the results of what the car is doing when each radio button is checked. When I run the program there is nothing in the textbox and just wanting to see if someone can take a quick look and what is wrong...

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Making_Decisions_Winforms1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        void DoTrafficLight(string color)
        {
            switch (color)
            {
                case "green":
                    textBox1.Text = "The car is moving!";
                    //tmrYellow.Enabled = true;
                    break;
                case "yellow":
                    textBox1.Text = "The car is slowing down!";
                    tmrYellow.Enabled = true;
                    break;
                case "red":
                    textBox1.Text = "The car has stopped!";
                    tmrYellow.Enabled = false;
                    break;
            }
        }

        private void greenRadioButton1_CheckedChanged(object sender, EventArgs e)
        {
            if (greenRadioButton1.Checked == true)
            {
                DoTrafficLight("green");
                
            }
        }

        private void yellowRadioButton1_CheckedChanged(object sender, EventArgs e)
        {
            if (yellowRadioButton1.Checked == true)
            {
                DoTrafficLight("yellow");
            }

        }

        private void redRadioButton1_CheckedChanged(object sender, EventArgs e)
        {
            if (redRadioButton1.Checked == true)
            {
                DoTrafficLight("red");
            }
        }

    }
}