Jun 02, 2016 - 03:04 PM
-If the jaws are not completely closed you will have problems. Sometimes the jaws are not big enough to completly close around a cable.
You can try using a fused jumper in place of a circuit like the dome lights and see if the probe reads correctly.
-You may also be seeing electrical noise in the workplace. Things like fluorescent lighting, noise from the vehicle ignition system, and so on, can introduce noise.