GxT Ferret 91 2-Channel Labscope - Manual (Page 19)

19
Electrical Tests
Apply Switch
Connect COM probe to the switch’s ground circuit, engine
block, or negative battery post. Connect the CH1 probe
to the switch’s signal circuit. Make sure power is switched
on in the circuit so that the sensor, device or circuit is
operational. The waveform should stay in a predetermined
voltage range for a given condition.
Alt Field Ctrl
Connect COM probe to the regulator ground circuit, engine
block, or negative battery post. Connect CH1 probe to
the Alternator Field Control signal from the PCM. Start
the engine and hold at 2500 RPM. Turn headlights or
other electrical loads on, or use battery load tester to vary
the load on the vehicle’s electrical system. When electrical
load is high, the waveform should go high to increase
alternator output. Frequency may also increase with
electrical load.
Battery B+ Supply V
Connect COM probe to the ground circuit, engine block,
or negative battery post. Connect the CH1 probe to the
power supply signal circuit. Make sure power is switched
on in the circuit so that the sensor, device or circuit is
operational. The waveform should stay in a predetermined
voltage range (amplitude) for a given condition.
Battery Test Cranking
Connect COM probe to the engine block, or negative
battery post. Connect the CH1 probe to the positive battery
post. Crank the engine for 10 seconds. The voltage should
not drop below 9.60 volts (at 70 Deg. F) during the test.