Articles about circuit testing
How to Test and Repair an Outlet Circuit Problem: Guide for Testing an Outlet Circuit, Inspect the Outlet Wiring, Electrical Troubleshooting.
Steps for Testing Electrical Power for a Pump Motor Circuit – Work you way back towards the controls and power source or electrical panel. It sounds like you lost one of the power legs of the motor circuit.
How to Identify Electrical Wiring for Lighting Circuits