Which two transducer and Y-cable are you wanting to know about Peter? There are two different possibilities here:
1. The Y-cable that uses the Si sonar and water temperature from the Si transducer and the 2D sonar from a DualBeam transducer. This is the AS-Si-DB-Y cable.
2. The Y-cable that uses the Right Si sonar, 2D sonar and water temperature from the Starboard side mounted Si transducer and the the Left side Si sonar from the Port side mounted Si transducer. This is the AS-Si-LR-Y cable.