Guardian 4389 Repair Manual page 103

DC CONTROL
TINUITY is measured in Step 8, replace the starter con-
tactor relay.
3. If battery voltage is measured in Step 6. proceed to
Test 49.
TEST 49- TEST STARTER CONTACTOR
DISCUSSION:
The starter contactor (SC) must energize and its
heavy duty contacts must close or the engine will not
crank. This test will determine if the starter contactor
is in working order.
PROCEDURE:
Carefully inspect the starter motor cable that runs
from the battery to the starter motor. Cable connec-
tions must be clean and tight. If connections are dirty
or corroded, remove the cable and clean cable termi-
nals and terminal studs. Replace any cable that is
defective or badly corroded.
Use a DC voltmeter (or a VOM) to perform this test.
Test the starter contactor as follows:
1. Connect the positive (+) meter test lead to the starter
contactor stud (to which the red battery cable connects).
Connect the common (-) meter test lead to a clean
frame ground. Battery voltage (12 volts DC) should be
indicated.
2. Now, connect the positive (+) meter test lead to the
starter contactor stud to which the starter motor cable
attaches (see Figure 6 or 7). Connect the common (-)
test lead to frame ground.
a. No voltage should be indicated initially.
b. Set the AUTO-OFF-MANUAL switch to MANU-
AL. The meter should now indicate battery volt-
age as the starter contactor energizes.
56
TO ECB
0
TO GROUND
TO BATTERY
Figure 6. The Starter Contactor (Single Cylinder Units)
PART 4
16
TO STARTER
STEP 2
TEST POINT
STEP 1
TEST POINT
13
TO FUSE (F1)
13
BATTERY
30
12V
CONNECTING
DIAGRAM
STARTER
CONTACTOR
STARTER
MOTOR
Figure 7. The Starter Contactor (V-twin Units)
RESULTS:
1. If battery voltage was indicated in Step 1, but NOT in
Step 2b, replace the starter contactor.
2. If battery voltage was indicated in Step 2b, but the
engine did NOT crank, go on to Test 50.
TEST 50- TEST STARTER MOTOR
CONDITIONS AFFECTING STARTER MOTOR
PERFORMANCE:
1. A binding or seizing condition in the starter motor bearings.
2. A shorted, open or grounded armature.
a. Shorted armature (wire insulation worn and
wires touching one another). Will be indicated
by low or no RPM.
b. Open armature (wire broken) will be indicated
by low or no RPM and excessive current draw.
c. Grounded armature (wire insulation worn and wire
touching armature lamination or shaft). Will be
indicated by excessive current draw or no RPM.
3. A defective starter motor switch.
4. Broken, damaged or weak magnets.
5. Starter drive dirty or binding.
DISCUSSION:
Test 47 verified that circuit board action is delivering
DC voltage to the starter contactor relay (SCR). Test
48 verified the operation of the SCR. Test 49 verified
the operation of the starter contactor (SC). Another
possible cause of an "engine won't crank" problem is
a failure of the starter motor.
SECTION 4.4
DIAGNOSTIC TESTS
16
STARTER
SWITCH
50
PERMANENT MAGNET
STEP 1
TEST POINT
STEP 2
TEST POINT
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