Here is what the manuall says. It sounds like you lost the tractor interface card.
Code 72 - Clock Chip Inoperative
The Display card cannot communicate with the clock
chip which is located on the Tractor Interface card.
System Response
Alarm Sounds
--
Energized (In) - LED = Heartbeat
Yes
1) Lift Power Ampmer I Energized (In) - LED = Heartbeat
- -
Performance Limits
Travel System
11 Tests to Run I None
1.0 mph
Lift/Lower System
How to Clear
Possible Cause:
Operational
Cycle the key switch OFF/ON.
Defective Tractor Interface card.
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