89 marathon starter problem

[Grandpadave]

I have been having problems with the starter not engaging when I press on the gas pedal. If I turn the engine over a bit sometimes it would work but now it has quit completely. I removed the starter and looked at the brushes and they don't look too worn. I'm looking for a wiring diagram so I can bench test the starter and if it works trace the wiring to see if some other component is failing.

Thanks in advance for any help with this issue.

[sccowboy]

Is the battery in known good working order? Here is a test procedure and the wiring diagram

Test Procedure 7 - Starter/Generator (Starter Function)

1. Place the neutral lock-out cam in the SERVICE position, put the forward and reverse lever in the NEUTRAL
position, and chock the wheels.

2. Check that wires are connected correctly and are tight. If they are not, rewire or tighten as necessary.

3. Disconnect the wires from all the terminals on the starter/generator. Then place the black (-) probe of a
multimeter, set to ohms (O), on the starter/generator housing (scratch through the paint to insure a
good ground). While holding the black probe against the housing, place the red (+) probe (one at a
time) on the A1, A2, F1, F2 and DF terminals respectively (Figure 12-25, Page 100). The readings
should be no continuity. If the readings are incorrect, the starter/generator will need to be removed
from the vehicle and disassembled by a qualified technician (See Removal of the Starter/Generator,
Page 107).
An incorrect reading from A1 or A2 terminal indicates three possible problems: 1) a grounded A1 or A2
terminal, 2) a grounded wire in the brush area, or 3) a grounded armature/commutator.
If the F1 or F2 reading is incorrect, it indicates a possible grounded F1 or F2 terminal or a grounded
field coil.
If the DF reading is incorrect, it indicates a possible grounded DF terminal or a grounded field coil.

4. Disconnect the ground wire from the A2 terminal and the green wire from the A1 terminal on the
starter/generator. Using a multimeter set to ohms (O), place the red (+) probe on the A1 terminal and
the black (-) probe on the A2 terminal. The reading should be continuity.
If the reading is incorrect, a possible open or poor contact in a brush assembly and/or open armature
windings maybe the cause. The starter/generator will need to be removed from the vehicle and disassembled
by a qualified technician (See Removal of the Starter/Generator, Page 107).

5. Disconnect the green wire from the F1 terminal and the white wire from the F2 terminal on the starter/
generator. Using a multimeter set on ohms (O), place the red (+) probe on the F1 terminal and the
black (-) probe on the F2 terminal. The reading should be continuity.
If the reading is incorrect, a possible open field coil or bad connections at terminals may be the cause.
The starter/generator will need to be removed from the vehicle and disassembled by a qualified technician

6. Disconnect the yellow wire from the DF terminal and the green wire from the F1 terminal on the starter/
generator. Using a multimeter set on ohms (O), place the red (+) probe on the DF terminal and the
black (-) probe on the F1 terminal. The reading should be between 4.5 to 5.5 ohms (O).
If the reading is incorrect, a possible grounded DF terminal and/or grounded field coil may be the
cause. The starter/generator will need to be removed from the vehicle and disassembled by a qualified
technician


Test Procedure 9 - Starter/Generator (Generator Function)

1. Place the neutral lock-out cam in the SERVICE position, put the forward and reverse lever in the NEUTRAL
position, and chock the wheels.

2. Check that wires are connected correctly and are tight. If they are not, rewire or tighten as necessary.

3. Disconnect the yellow wire from the DF terminal on the starter/generator. Cover the connector on the
yellow wire to make sure the yellow wire will not short to ground. Then, using a jumper wire, ground the
DF terminal to the A2 terminal. Using a multimeter set to Volts DC (20v range), place the red (+) probe
on the positive (+) post of the battery, and place the black (-) probe on the negative (-) post. Turn the
key switch to the ON position, and depress the accelerator to start the engine. Run the engine at full
governed speed. The reading should show voltage rising on the meter. If voltage rises, see Test Procedure
10 - Voltage Regulator. If the voltage does not rise, see Starter/Generator Repair, Pages 107-116.

4. Reconnect the yellow wire to the (DF) terminal on the starter/generator.


Test Procedure 10 - Voltage Regulator:

1. Place the neutral lock-out cam in the SERVICE position, put the forward and reverse lever in the NEUTRAL
position, and chock the wheels.

2. Check that the wires are connected correctly and are tight. If they are not, rewire or tighten as necessary.

3. Start the engine and check engine-governored RPM. The reading should be between 2670-2730 RPM.
If it is not, adjust the accelerator cable at the electrical component box (See Fuel System, Section 14).

4. With the battery in good condition and fully charged, and with proper ventilation, run the engine for several
minutes to bring the voltage regulator to operating temperature, then release the accelerator pedal
to stop the engine. Using a multimeter set to DC volt (DCV), place the red (+) probe on the large post of
the solenoid with the red wire from the voltage regulator attached. Place the black (-) probe on the negative
(-) post of battery. Depress the accelerator to start the engine, and run it at full governed speed. If
the reading is between 14.7 and 15.3 volts, the regulator is good. If the reading is lower than 14.7 volts
but rising steadily, check battery condition (See Hydrometer Test, Page 12. If the reading is lower
than 14.7 volts and not rising, and the starter/generator is good; or if the reading is over 15.3 volts and
continues to rise, replace voltage regulator

[Grandpadave]

Thanks for all the information SCCOWBOY. Now I can do some exploring and see what's going on.

Have a great day.

Dave

[Grandpadave]

Thank you so much SCCOWBOY for the documents and wiring schematic. This morning I tested out the starter / generator and found the problem. When the starter was assembled two of the wires in the brush assembly were pinched in the end cap housing. I relocated them and patched the wire casing and everything works perfectly now.

[sccowboy]

Glad to hear you got it worked out.