Rheem MPi 551 Series Owner's Manual And Installation Instructions page 35

Tank Sensor Cable Connection: Insert the tank sensor cable plug to the connector on the underside of
24.
the control box.
The plug is polarised and can only be inserted one way.
Ensure the plug fully engages the locking feature on the connector.

25. Power Cable Connection: Insert the four pin power cable plug to the connector on the underside of the
control box.
The plug is polarised and can only be inserted one way.
Positioning of Water Heater: Complete final positioning of the water heater.
26.
Ensure the heat pump module is firmly seated on the level slab or solid base.
Steps 24 and 25
connect power cable and tank sensor cable
35
HEAT PUMP AND TANK ASSEMBLY