How to Connect to an external table via EBC using Siebel Web Client

Create Table Definition

Import schema using External Table Schema Import Wizard
Set table/column properties as necessary
Define data source
Set optional table properties

Set a column having System Field Mapping attribute set to Id. This can lead to unexpected behavior and even to make the application not work as expected.

The data source attribute is defined for both tables and apparently you are not using the optional table properties.

Configure External Business Component

Specify Data Source property

Specify Component parameters

Configure new data source in Server Admin view
Navigate to Administration - Server Configuration > Enterprises > Profile Configuration
Copy an existing InfraDatasources named subsystem. Use ServerDataSrc (dont pick GatewayDataSource)
Set the Name property to the Data Source name configured in Siebel Tools

Update profile parameters to correspond to the external RDBMS
DSConnectString data source connect string
DSSQLStyle database SQL type
DSTableOwner data source table owner
DSUsername default user name used for connections
DSPassword default password used for connections

Start Reconfiguration of server component
Update server component to use new data source
Update OM - Named Data Source name parameter
Append new data source Alias name (the one without spaces) to the existing list in the Value property
Commit Reconfiguration of server component
Verify reconfiguration