SDE Ltd. 429 Test Box S3033

The SDE 429 Test Box is a specific type of avionics ground support equipment that is used for testing systems that use the ARINC 429 data bus standard. 

It allows a technician to manually connect or route different ARINC 429 signals (or "phases") to specific pins on the large circular connector using the front-panel switches.

Used during maintenance or installation to troubleshoot wiring issues, simulate system inputs, or verify system functionality.