1674 DIESEL TRUCK ENGINE Electrical System Caterpillar

Electrical System
1.1. Battery
2.1. Starting System
3.1. General Reconditioning
4.1. Glow Plugs
5.1. Charging System

The following topics describe care and maintenance of the electrical system components. These components functioning together produce the energy needed for operating the electrical equipment on the truck and each is dependent upon the others for satisfactory operation. In the event of failure or improper operation, it is essential to check the entire electrical system as a defect in one component can cause damage to another.

Many electrical system problems can be traced to loose or corroded connections. Keep connections tight and make sure the wiring insulation is in satisfactory condition. Most of the electrical system testing can be performed on the vehicle. It should be remembered, if a malfunction is found on vehicle test, the component must be removed for further testing, repair or replacement.

NOTE: Some installations may have electrical components not furnished by AVSpare. Consult the vehicle manufacturer's manual for maintenance procedures.


Every 10,000 miles check the electrolyte level of each cell and the general condition of the battery. Maintain the electrolyte level to the base of each vent well. The make-up water must be one of the following (in order of preference):

1. Distilled water.
2. Odorless, tasteless drinking water.
3. Iron free water.
4. Any available water.

------ WARNING! ------

Never add acid or electrolyte.


CLEANING BATTERY: Mix a weak solution of baking soda and water. Apply the solution with a soft bristle brush. Be careful not to get cleaning solution into the battery.

Thoroughly rinse the battery and battery tray with clean water. Apply grease to the battery cable clamps and terminals and to all threads.


TESTING THE ELECTROLYTE SOLUTION: The general condition of a battery can be determined by measuring the specific gravity of the electrolyte solution and adjusting the reading to 80°F (27°C). If the electrolyte level is too low to allow taking a hydrometer reading, add make-up water to the correct level and then charge the battery 2 to 4 hours before taking a reading.


1. Insert the hydrometer into a cell. Fill the hydrometer barrel while holding it vertically. The float must not drag on the wall of the barrel.
2. Read the hydrometer:

1.250 or above - fully charged battery cell

1.250-1.225 - full to half charged battery cell

1.225-1.150 - half to low charged battery cell

Below 1.150 - dead cell

1.000 - water

3. Test each cell in the same manner.
4. If there is more than .050 (50 gravity points) variation between the highest and lowest reading, the battery should be replaced.
5. Adjust the readings to 80°F (27°C).
a. For every 10F° (5,5C°) the electrolyte temperature is above 80°F (27°C), add .004 (4 gravity points) to the specific gravity readings.
b. For every 10F° (5,5C°) the electrolyte temperature is below 80°F (27°C), subtract .004 (4 gravity points) from the specific gravity reading.

The corrected reading is of most importance during cold weather when the hydrometer reading is always corrected to a lower specific gravity reading. A low reading signifies the battery has less available power to crank the engine and that booster batteries may be required.

VOLTAGE TEST (AFTER LOAD): A load test should be made on a battery that discharges very rapidly when in use. To do this apply a resistance of three times the ampere/hour rating of the battery across the battery main terminals. Allow the resistance to discharge the battery for 15 seconds and immediately test the battery voltage. A 6 volt battery in good condition will test 4.5 volts; a 12 volt battery in good condition will test 9 volts and a 24 volt battery will test 18 volts.

Starting System

Use a D.C. voltmeter to locate starting system components which do not function.

Turn the key switch ON. Turn the HEAT-START switch to the START position. Starting motor solenoid operation is audible as the starter motor pinion engages with the ring gear on the engine flywheel. The solenoid operation should also close the electric circuit to the starting motor. Attach one voltmeter lead to the solenoid terminal that is connected to the starting motor. Ground the other lead. Turn the HEAT-START switch to START and observe the voltmeter. A battery voltage reading indicates the malfunction is in the starting motor. It must be removed for further testing. No voltmeter reading indicates that the solenoid contacts do not close. The solenoid must be repaired or the starter pinion clearance should be adjusted to .36 in. (9.14 mm). See topic PINION CLEARANCE ADJUSTMENT.

A starting motor solenoid that will not operate may not be receiving battery current. Attach one lead of the voltmeter to the solenoid battery cable connection. Ground the other lead. No voltmeter reading indicates a faulty circuit from the battery. A voltmeter reading indicates further testing is necessary.

Continue the test by attaching one voltmeter lead to the starting motor solenoid small wire terminal and the other lead to ground. Observe the voltmeter and turn the HEAT-START switch to START. A voltmeter reading indicates that the malfunction is in the solenoid. No voltmeter reading indicates that either the series-parallel switch is the fault or the HEAT-START switch does not close when turned to the START position.

Attach one lead of the voltmeter to the HEAT-START switch battery wire terminal and ground the other lead. A voltmeter reading indicates a defective switch. No voltmeter reading indicates further testing of the series-parallel switch is necessary.

A starting motor that operates too slow can be overloaded by excessive mechanical friction within the engine being started. Slow starting motor operation can also be caused by shorts, loose connections and/or excessive dirt within the motor.

PINION CLEARANCE ADJUSTMENT: Whenever the solenoid is installed, the pinion clearance should be adjusted. The adjustment should be made with the starting motor removed.

Bench test and adjust the pinion clearance at installation of solenoid as follows:


1. Install the solenoid without connector from the MOTOR terminal on solenoid to the motor.
2. Connect a battery, of the same voltage as the solenoid, to the terminal marked SW.
3. Connect the other side of battery to ground terminal or to solenoid frame.



4. MOMENTARILY flash a jumper wire from the solenoid terminal marked MOTOR to the frame or ground terminal. The pinion will shift into cranking position and will remain there until the battery is disconnected.
5. Push pinion towards commutator end to eliminate free movement.
6. Pinion clearance should be .36 in. (9,14 mm).
7. Adjust clearance by removing plug and turning shaft nut.

General Reconditioning

Approximately every 200,000 miles, the starter should be removed so that it may be completely disassembled, washed and have all parts replaced that show evidence of being unsatisfactory for reason of wear. Do not use a degreaser or high temperature cleaning method when cleaning parts of the starter.

No periodic service is indicated for the electric starter brushes between general reconditioning periods. The brushes should only be inspected after removal of the starter from the engine and removal of the commutator end bearing frame. The electric starter commutator end and drive end bearings are equipped with wicks for lubrication purposes. The wicks should be saturated with oil whenever the electric starter is removed or disassembled.

It is suggested that cleaning and reconditioning be entrusted to your authorized dealer.

Glow Plugs

TESTING GLOW PLUGS: Glow plugs can be checked with an ammeter. Disconnect the wire lead from the glow plug terminal on the HEAT-START switch. Install an ammeter, in series, between the disconnected lead and the terminal on the switch. Observe the ammeter with the HEAT-START switch turned to the HEAT position. Each 12 volt glow plug draws approximately 10 amperes. The ampere draw of one glow plug multiplied by the number of engine cylinders will be the total ampere draw of the glow plugs in the engine. A low reading is an indication of one or more defective glow plugs. Disconnect one glow plug lead at a time and observe the ammeter with the switch turned to HEAT. The disconnected glow plug that does not change the ammeter reading is the defective glow plug.

REPLACING GLOW PLUGS: To remove a defective glow plug disconnect the lead from the glow plug and unscrew the glow plug from the precombustion chamber. Apply anti-seizure compound to the thread of a new glow plug and install the glow plug into the precombustion chamber. Tighten it to a torque of 10 to 12 pounds feet.

When no ammeter reading is obtained, test the HEAT-START switch. Attach one lead of the voltmeter to the glow plug wire terminal on the HEAT-START switch and the other lead to the ground. Observe the voltmeter and turn the switch to HEAT. No voltage indicates that the HEAT-START switch is defective.

Charging System

ALTERNATOR REGULATOR: The alternator regulator is adjusted at the factory for average operating conditions and may require readjustment to provide the proper charging rate for the particular operating conditions.

The condition and state of charge of the battery at each regular inspection will indicate if the alternator is operating efficiently. An adjustment is necessary when the battery is always in a low state of charge or an excessive amount of water must be added to the battery (more than one ounce of water per cell per week or per every 50 service hours).

When the alternator is either overcharging the battery or undercharging, the alternator charging rate can be adjusted. Remove the hollow head screw from the cover of the alternator regulator and use a screwdriver to turn the inside adjustment. Turn the adjustment toward the "+" to increase or toward the "-" to decrease the alternator charging rate.

CHARGING ALTERNATOR: The charging alternator is designed to give long service periods with a minimum amount of maintenance. Grease reservoirs for the two ball bearings on which the rotor is mounted, eliminate the need for lubrication. Repack bearings when alternator is reconditioned.

Never operate the charging alternator with an open circuit between it and battery.


Do not attempt to polarize the alternator. If an accidental connection is made between the "+" terminal and either one of the "F" terminals on the alternator, the rectifiers in the alternator and the transistors in the regulator will be damaged.

ALTERNATOR BELTS: Every 10,000 miles examine the drive belts for wear and replace if they show signs of wear.

If one belt in a set requires replacement, always install a new matched set of belts - never replace just the worn belt. If only the worn belt is replaced, the new belt will be carrying all of the load - as it will not be stretched as much as the older belts - and all of the belts will fail in rapid succession.

ADJUSTMENT: Check new belts after the first 500 miles and every 10,000 miles thereafter for adjustment. To check belts - apply 25 lbs. (11,5 kg) force midway between the pulleys. Correctly adjusted belts will deflect 1/2 in. (12,5 mm) to 3/4 in. (19 mm) for the first check. Maintain later adjustments at 7/8in. (23 mm).


To adjust: Loosen mounting bolts and locknut on adjusting bolt. Turn adjusting nuts to increase or decrease alternator belt tension. Tighten locknut and mounting bolts.

If belts are operated too loose they will slap causing unnecessary wear to the belts and pulleys. Belt slipping may cause the alternator to operate at a below normal rate and possible failure of the electrical system.

If the belts are too tight, unnecessary stresses are placed upon the pulley bearings and belts which might shorten the life of both.


Wiring Diagrams: The diagrams are furnished if it becomes necessary to distrrb the electrical equipment for reconditioning or parts replacement.

NOTE: Some installations may have a different diagram because of the wiring circuit being integral with the vehicle. Consult the vehicle manufacturer's service manual for wiring diagram if this condition exists.

24 Volt Starting With 12 Volt Glow Plugs

12 Volt Starting With 12 Volt Glow Plugs