How to compare values entered in template field textbox

hi, i have a detailsview data control connected to a datasource. i converted all the bound fields to item templates and they have all been converted to textboxes. i need to compare values entered in one textbox and output the value in the other. I have attached a snippet of the code below. but its not working. pLease help.

<asp:DetailsView ID="DetailsView2" runat="server" AllowPaging="True" AutoGenerateRows="False"
    DataKeyNames="ID" DataSourceID="SqlDataSource1" Height="113px" Style="margin-right: 237px"
    Width="614px" DefaultMode="Insert" CellSpacing="3" GridLines="Vertical">
    <Fields>
        <asp:BoundField DataField="ID" HeaderText="ID" InsertVisible="False" ReadOnly="True"
            SortExpression="ID" />
        <asp:TemplateField HeaderText="Warranty" SortExpression="Warranty">
            <EditItemTemplate>
                <asp:TextBox ID="TextBox3" runat="server" Text='<%# Bind("Warranty") %>'></asp:TextBox>
            </EditItemTemplate>
            <InsertItemTemplate>
                <asp:TextBox ID="TextBox3" runat="server" Text='<%# Bind("Warranty") %>'></asp:TextBox>
            </InsertItemTemplate>
            <ItemTemplate>
                <asp:Label ID="Label3" runat="server" Text='<%# Bind("Warranty") %>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Warranty Score" SortExpression="Warranty Score">
            <EditItemTemplate>
                <asp:TextBox ID="TextBox4" runat="server" Text='<%# Bind("WarrantyScore") %>'></asp:TextBox>
            </EditItemTemplate>
            <InsertItemTemplate>
                <asp:TextBox ID="TextBox4" runat="server" Text='<%# Bind("WarrantyScore") %>'></asp:TextBox>
            </InsertItemTemplate>
            <ItemTemplate>
                <asp:Label ID="Label4" runat="server" Text='<%# Bind("WarrantyScore") %>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
    </Fields>
</asp:DetailsView>

Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    If Textbox3.Text.ToString = "Yes" Then
            Textbox4.Text = "1"
        Else
            Textbox4.Text = "2"
    End If
End Sub