instantiate a Data Access Layer once and have it exposed to all Classes

Hi

Background:
new to C#
using VSpro
using Windows Forms
Built Classes for BusinessLogic, DataAccess,Customers, Suppliers, Parts etc.

What I need to do :
1) separate the Data Access(Da) Layer and Business Logic(Bl) Layer from the UI
2) Have only 1 global instantiation of the BL object and the DA object

Wjat I did:
On the Business Logic Side I have done so with the Following:
On MainForm I have the the following that will give me one entry point to the Business Logic (BL)Object.


Instantiate the BusinessLogic (Bl) Class:

public partial class MainForm : Form
{

public static BusinessLogic Bl = new BusinessLogic();


public MainForm()
{
InitializeComponent();
}

I can address any Method in the BL Object using something like MainForm.Bl.SelectACustRecord(CustRec);.
This works fine for all of my forms.

PROBLEM:
I cannot think of a way to Instantiate the DataAccess Class once so I can address this class in all
of my other classes. "Customer.cs","Parts.cs" etc unless I instantiate the DA Object in each Class as in :


class Customer : Business
{
public DataAccess Da = new DataAccess();
double _creditLimit;

public Customer()
{


}

WHAT I HAVE DONE TO DATE:
1)In the BL class I instantiate the Da class - no go
2)Instantiate the Da in each Class this allows me to address DA but
When I fire "public DataAccess Da = new DataAccess(); " the DataAccess Constructor fires
and the SQL Connection opens.
as in :

public class DataAccess
{
private string connectionString;
private SqlConnection connection;

public DataAccess()
{

connectionString = "Data Source=Server;Initial Catalog=Server.MyDB_DB.dbo;Integrated Security=True";
connection = new SqlConnection(connectionString);
}

Hope this makes sense.
Any suggestion would be greatly appreciate

Thanks in advance

Allan