I routinely use a several Amp AC current generator to chase down and find resistive connections (and ground loops) along the ground path in an aircraft (airframe). For weight saving, most aircraft power circuits use the airframe as a return path for distant loads. The currents flowing along the airframe cause a large voltage drop (some times approaching a few Volts) between different parts of an airframe. If low-level circuits (instrumentation, audio) are grounded to the airframe in more than one place, the resulting ground loop can induce huge problems into those low-level circuits.
For example, I am frequently called upon to get alternator-whine out of aircraft audio/intercom/stereo music systems. Since running an aircraft engine and prop in a shop (to spin an alternator) is problematic , I get an unregulated, un-filtered battery charger and hook it across the alternator. The 120Hz ripple charging current from the charger takes the same path along the airframe as would the 1000+Hz ripple current from the alternator if it were turning. Now I can hear the 120Hz from the charger in the aircraft audio circuits to help find the source of the ground loop. I can also just take an aircraft headset, and using two clip leads connected to airframe ground at disjoint locations, I can "hear" the voltage induced by the charger ripple current flowing in the part of the airframe between the clip lead connection points. I suppose a sensitive AC milliVoltmeter (lock-in amplifier) would do the same thing, but the headphones work fine...
