Vanguard BIG BLOCK M540000, Repair Manual, Page: 39 / 168

4. Connect the RED test lead probe to the POSSITVE
terminal of the battery, and the BLACK test lead probe to
the NEGATIVE terminal of the battery.
5. Disconnect BOTH ignition wires from the spark plugs and
secure to avoid arcing.
NOTE: On gaseous-fueled standby generator engines, turn
fuel supply OFF.
6. Crank the engine for 15 seconds and monitor the voltage
drop on the multimeter display.
If the observed battery voltage reading remains ABOVE
9.6 volts the battery is OK. If the observed battery
voltage reading is EQUAL TO OR BELOW 9.6 volts ,
replace the battery with new before continuing.
Test Engine Wiring Harness
Test Engine Wiring
If equipped with an EFI or EFI-ETC engine, consult the
appropriate EFI and EFI-ETC Service & Diagnostics
manual for engine wire harness testing, pin-outs, and wiring
schematics.
If equipped with a carbureted or gaseous-fueled engine,
the wiring harness consists of a ground wire, a wire with a
diode for each armature, a wire for the anti-afterfire solenoid,
and a wire for the oil pressure sensor. Depending on your
engine configuration and equipment, additional wiring may
be present. For testing, service and troubleshooting of the
equipment wiring harness, see the equipment service and
repair manual.
Testing Wire Harness Diodes
1. Obtain a digital multimeter with test leads. See Special
Tools List in this section.
2. Insert the RED test lead into the volt/ohm receptacle on
the meter.
3. Insert the BLACK test lead into the COM receptacle on
the meter.
4. Select the DIODE TEST position on the meter.
5. Connect the RED test lead clip to the BLACK wire pin in
the engine harness connector (usually pin 5 on a 6-pin
connector).
6. Connect the BLACK test lead clip to the armature
electrical connector.
a. Observe the multimeter display, if the reading is
between 0.6 and 0.7 volts , then the diode is healthy
and working correctly.
7. Reverse the meter test lead clips so that the RED test
lead clip is attached to the armature connector and the
BLACK test lead clip is attached to the engine harness
connector.
a. Observe the multimeter display. The meter should
red OL if the diode is healthy and working correctly.
If the meter shows values different that the above values,
the diode is defective. The diode can be either open or
short.
An OPEN diode means that current cannot flow in
either direction. The meter will read OL in both testing
positions.
A SHORTED diode means that current flows in both
directions and the voltage drop across the diode will be
between 0 and 0.4 volts .
8. Test the other armature wiring and diode. Repeat steps 1
- 7.
Test Engine Wire Harness Continuity
A continuity test is a simple but effective test to determine
whether the component wire(s) are damaged or broken. This
condition would prevent a specific component from operating
correctly, or at all.
1. Obtain a digital multimeter. See
Special Tools List in this
section.
2. Connect the RED test lead into the volt/ohm
receptacle on the meter.
3. Connect the BLACK test lead into the COM receptacle
on the meter.
4. Set the multimeter to read CONTINUITY. Usually marked
with the Ohm symbol. Set the range to the lowest value.
5. Select the specific component wire to be tested.
Disconnect the wire and connector from the component.
6. Attach the RED test lead clip to the component wire
electrical connector.
7. Attach the BLACK test lead clip to the terminating end
of the component wire, usually within a wiring harness
connector or main engine harness connector.
8. Allow the meter reading to stabilize, then observe the
meter display.
a. A meter displaying
0 Ohms indicates perfect
continuity.
b. A meter displaying less than 1 Ohm has good
continuity.
c. A meter displaying 1 or higher may be an indication
high resistance. Check the electrical terminals being
tested for dirt or corrosion.
d. A meter displaying OL indicates that NO continuity
exists. Check the wire for breaks, replace as
necessary.
40 vanguardpower.com