Instructions

8
With power on, LD3 (LOW LEVEL) should illuminate, showing that
everything works.
Put a link across low-level sensor S2, and LD2 should illuminate.
Add another link across high-level sensor S1, and LD1 and LD4 should
both illuminate.
Remove the link across input sensor S1, now LD2 should illuminate
together with LD4 (relay on).
Remove the link across input sensor S2, now only LD3 should illuminate.
Testing
LD4
S1
LD1 LD2 LD3
S2
LD4
S1
LD1 LD2 LD3
S2
LD4
S1
LD1 LD2 LD3
S2
LD4
S1
LD1 LD2 LD3
S2
Fig 3.0
Fig 3.1
Fig 3.2
Fig 3.3