Binding a combobox in a datagrid

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XAML

I can bind a DataGridComboBox using the SelectedValueBinding and it works ok. My XAML coded properties for DataGridComboBoxColumn

Header="Empl ID"
ItemsSource="{Binding Source={StaticResource csv}}"
DisplayMemberPath="EmployeeID"
SelectedValuePath="EmployeeID"
SelectedValueBinding="{Binding EmployeeID, UpdateSourceTrigger=PropertyChanged}">

But when I try to bind the Combobox within a DataGridTemplateColumn, the "SelectedValueBinding" is not available. Following is my last updated code. When the window is opened the combobox opens to the first record, but should be the record corresponding to the row in the grid.

DataGridTemplateColumn Header="Empl ID">
    DataGridTemplateColumn.CellTemplate>
          DataTemplate>
              ComboBox ItemsSource="{Binding Source={StaticResource csv}}" 
                         DisplayMemberPath="EmployeeID"
                         SelectedValuePath="EmployeeID"
                         SelectedValue="{Binding Path=EmployeeID, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                         TextSearch.TextPath="EmployeeID">

Any Suggestions?

Thanks

What I have tried:

I've tried numerous things, with the last being adding the TextSearch property.