[header] How to use an ohmmeter [title] Disconnect completely and/or turn off all power to the circuit you are testing. [step] You must have a completely dead wire or circuit in order to ensure accuracy in measurement, as well as your own safety. Your ohmmeter will supply the voltage and current for your circuit so no other power is necessary. 
As the instructions for our blue point volt/ohmmeter state, testing a powered circuit can " cause damage to the meter, circuit, and * you *. " [title] Select an ohmmeter suitable for your project.