how do i access a dropdownlists selected value in a datagrid edititemtemplate column from the select

[Dave M]

i am trying to trap the value of one dropdownlist (in a datagrid
edititemtemplate column) at the time its selectedindexchanged event
fires and use its value to query a db and rebind a second dropdownlist
(in a second datagrid edititemtemplate column).

here's my code:

<td width="9"><asp:datagrid id="dgManageVehicles" runat="server"
Width="472px" AutoGenerateColumns="False" CellSpacing="1"
CellPadding="3" BackColor="White" BorderWidth="2px"
BorderStyle="Ridge" BorderColor="White" AllowSorting="True"
DataKeyField="VehicleID" Height="216px">
<SelectedItemStyle Font-Bold="True" ForeColor="White"
BackColor="#9471DE"></SelectedItemStyle>
<EditItemStyle Font-Size="Smaller" Font-Names="Arial"
BorderWidth="2px" ForeColor="Lime" BorderStyle="Double"
BorderColor="Black" BackColor="Aqua"></EditItemStyle>
<ItemStyle Font-Size="9px" Font-Names="Verdana"
ForeColor="White" BackColor="Black"></ItemStyle>
<HeaderStyle Font-Size="10px" Font-Names="Verdana"
Font-Bold="True" ForeColor="#E7E7FF" BorderStyle="None"
BackColor="Black"></HeaderStyle>
<FooterStyle ForeColor="Black"
BackColor="#C6C3C6"></FooterStyle>
<Columns>
<asp:BoundColumn Visible="False" DataField="DealerID"
HeaderText="DealerID"></asp:BoundColumn>
<asp:BoundColumn Visible="False" DataField="VehicleID"
HeaderText="VehicleID"></asp:BoundColumn>
<asp:TemplateColumn HeaderText="Make">
<ItemTemplate>
<asp:label id="Label1" runat="server"
ForeColor="White" Font-Names="Verdana">
<%# DataBinder.Eval(Container.DataItem,
"VehicleMake") %>
</asp:label>
</ItemTemplate>
<EditItemTemplate>
<asp:dropdownlist id=ddlEditMakes runat="server"
Font-Names="Verdana" BackColor="White" Font-Size="10px"
AutoPostBack="True" DataSource="<%# GetMakes %>"
DataTextField="MakeDesc" DataValueField="MakeID"
OnSelectedIndexChanged="MakeIndexChange_Command" SelectedIndex='<%#
GetMakeSelIndex(DataBinder.Eval(Container.DataItem, "VehicleMake")) %>'</asp:dropdownlist>
</EditItemTemplate>
</asp:TemplateColumn>
<asp:TemplateColumn HeaderText="Model">
<ItemTemplate>
<asp:label id="Label2" runat="server"
ForeColor="White" Font-Names="Verdana">
<%# DataBinder.Eval(Container.DataItem,
"VehicleModel") %>
</asp:label>
</ItemTemplate>
<EditItemTemplate>
<asp:dropdownlist id="ddlEditMakeModel"
runat="server" Font-Names="Verdana" BackColor="White"
DataTextField="MODEL_DESCRIPTION" DataSource='<%#
GetMakeModels(DataBinder.Eval(Container.DataItem, "VehicleMake")) %>'
AutoPostBack="False" Font-Size="10px">
</asp:dropdownlist>
</EditItemTemplate>
</asp:TemplateColumn>
<asp:BoundColumn DataField="RegYear"
HeaderText="Registration Year"></asp:BoundColumn>
<asp:BoundColumn DataField="Engine_CC"
HeaderText="Engine Size (cc)"></asp:BoundColumn>
<asp:BoundColumn DataField="Body_desc"
HeaderText="Body Type"></asp:BoundColumn>
<asp:BoundColumn DataField="Colour"
HeaderText="Colour"></asp:BoundColumn>
<asp:BoundColumn DataField="Mileage"
HeaderText="Mileage"></asp:BoundColumn>
<asp:TemplateColumn HeaderText="New">
<ItemTemplate>
<asp:Checkbox id=chkIsNew runat="server"
Checked='<%# DataBinder.Eval(Container.DataItem, "IsNew") %>'
enabled="false">
</asp:Checkbox>
</ItemTemplate>
<EditItemTemplate>
<asp:Checkbox id=ChkUPDIsNew runat="server"
Checked='<%# DataBinder.Eval(Container.DataItem, "IsNew") %>'>
</asp:Checkbox>
</EditItemTemplate>
</asp:TemplateColumn>
<asp:BoundColumn DataField="Carfinderprice"
HeaderText="Car Finder Price"></asp:BoundColumn>
<asp:BoundColumn DataField="standardprice"
HeaderText="Price"></asp:BoundColumn>
<asp:BoundColumn DataField="lastupdated"
ReadOnly="True" HeaderText="Last Updated"></asp:BoundColumn>
<asp:ButtonColumn Text="Delete"
ButtonType="PushButton" CommandName="Delete"></asp:ButtonColumn>
<asp:EditCommandColumn ButtonType="PushButton"
UpdateText="Update" CancelText="Cancel"
EditText="Edit"></asp:EditCommandColumn>
</Columns>
<PagerStyle HorizontalAlign="Right" ForeColor="Black"
BackColor="#C6C3C6"></PagerStyle>
</asp:datagrid></td>

Ive Got a custom event call :-

OnSelectedIndexChanged="MakeIndexChange_Command"

Q, what 'eventargs' do i need to pass to trap the selected value of the
first dropdown from the datagrid and use it to rebind the second
dropdown?