Magnetic Switch Circuit Test - Borg Warner Delco Remy 28MT Diagnostic Procedures Manual

Test
1. Push starter button with key on.
2. Turn on and adjust carbon pile to 100 amp load (60 amp if
24-volt system).
3. Read and record voltage (V9) on voltmeter.
Connect
1. Positive lead of digital voltmeter set on low scale to switch
wire lead to which carbon pile is connected.
2. Negative lead of voltmeter to other large terminal on
magnetic switch.
Test
1. Push starter button with key on.
2. Turn on and adjust carbon pile to 100 amp load (60 amp if
24-volt system).
3. Read and record voltage (V10) on voltmeter.
4. Add voltage loss (V10) to voltage loss (V9), previously
recorded, to get total wire voltage loss.
5. Total wire voltage loss shall not exceed:
12-volt system - 0.8 volt
24-volt system - 1.8 volt
6. Replace and repair wiring and connections if voltage loss is
excessive.
Perform the following test only if the magnetic switch closed in
preceding tests.
3-16. MAGNETIC SWITCH CONTACTOR TEST
With carbon pile connected as instructed in previous Starter
Solenoid Circuit Test, proceed as follows:
Connect
1. Digital voltmeter set on low scale across large terminals of
magnetic switch. Battery voltage will show immediately.
Test
1. Push starter button with key on. Voltage will read zero.
2. Turn on and adjust carbon pile to 100 amp load (60 amp if
24-volt system).
3. Read and record voltage (V11) across magnetic switch on
voltmeter, then release starter button.
NOTE
(See Figure 3-6).
4. Magnetic switch contactor voltage loss (V11) shall not exceed
0.2 volts for 12- or 24-volt system.
5. Replace magnetic switch if contactor voltage loss is excessive.
FIRST
WIRE
LOSS (9)
FIGURE 3-6. Solenoid Circuit Wiring
and Contactor Test
3-17. TEST COMPLETION.
Turn carbon pile off. Remove
carbon pile and voltmeter from circuit. Leave solenoid S wire
disconnected and temporarily taped for insulation at the terminal.

3-18. MAGNETIC SWITCH CIRCUIT TEST

This test must be performed using full voltage of the system. If
a 24-volt system was temporarily connected to a 12-volt system
for a previous test, proceed to the Alternator Wiring Test,
paragraph 3-26. Then, return to this test after the batteries have
been reconnected to the 24-volt system. Note that the lead to
the S terminal on the starter solenoid remains disconnected from
previous tests (See Figure 3-7).
CONTACTOR
LOSS (11)
SECOND WIRE LOSS (10)
CARBON PILE
DP-1024
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