Engine Wiring Harness; Testing Ground Wires; Digital Multimeter; Diode Failure Diagnosis - Generac Power Systems GTH760 Service Manual

GeNerAl INForMATIoN
Generac GTH/GTV-760/990 OHVI V-Twin engines use a mag-
neto ignition: an ignition coil with a self-contained transistor
module (no moving parts). Two magneto ignition coils are
used, with a flywheel containing a permanent magnet.
NOTE: The magneto ignition system requires a minimum
of 250 RPM to produce a consistent spark.

eNGINe wIrING HArNeSS

The engine wiring harness consists of a ground wire with a
diode for each ignition coil and a separate wire for the carbu-
retor solenoid. The engine ground wires are connected to the
wiring harness provided by the equipment manufacturer.
NOTE: Newer models will have the diodes built into
the ignition coils or spark plug leads. Check the wire
harness. If there are no diodes in the harness, perform
test on the coil ground terminal.
See Figure 2-4.

TESTING GROUND WIRES:

use a Digital Multimeter (Figure 2-1) to test the
ground wires.
The following test will be made with the meter in the Diode
Test position.
In the Diode Test position, the meter will display the forward
voltage drop across the diode(s). If the voltage drop is less
than 0.7 volts, the meter will "Beep" once as well as display
the voltage drop. A continuous tone indicates continuity
(shorted diode) An incomplete circuit (open diode) will be
displayed as "OL."
Figure 2-1. Digital Multimeter
1. Insert RED test lead into
2. Insert BLACK test lead into the "COM" receptacle
in meter.
3. Rotate selector to
4. Insert RED test lead clip into connector "A" (Figure 2-2).
5. Touch BLACK test lead probe to terminal "B."
6. Now repeat test for terminal "C." Results must be
7. Replace wiring if defective.
8. If wiring tests good, proceed to IGNITION COILS section
Note: See "Diode Failure Diagnosis", Figure 2-3.
receptacle in meter.
2-1
(Diode Test) position.
Leave attached for remainder of test.
a. If meter "Beeps" once, diode is OK.
b. If meter makes a continuous tone, diode is defective
(shorted). Replace ground harness.
c. If meter displays "OL," diode is defective (open). Replace
ground harness.
the same.
to replace defective coil.
ENGINE
GROUND
HARNESS
A
CYL #1
B
CYL #2
POSITIVE METER
TEST LEAD
Figure 2-2. Testing Ground Wire
SwITCH oN TurNed oFF
Engine Runs Shuts Off OK
On 1 Cylinder
Engine Runs Only One
(Both Cylinders) Cylinder
Won't Run
(No Spark)
Engine Runs Engine Won't
(Both Cylinders) Shut Off
Figure 2-3. Diode Failure Diagnosis
SeCTIoN 2: IGNITIoN
2
IGNITION
GROUND
C
WIRE STUD
NEGATIVE METER
TEST LEAD
CAuSe
1 Closed Diode
1 Open Diode
2 Closed Diodes
2 Open Diodes