824 TRACTOR Electrical System Caterpillar

Electrical System
1.1. Battery
2.1. Charging Alternator (24 and 12 Volt Systems)
3.1. Wiring

The basic electrical system is composed of a battery, a charging alternator, and wiring to all the components in the system.

These components functioning together produce the electricity for the electrical equipment on the machine 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.

The topics which follow describe the proper maintenance of the components to assure satisfactory operation of the electrical system.


Every 50 service hours, or whenever ammeter readings indicate a condition of over or under charging, the following attention should be given to insure high efficiency and maximum service life of the battery.

Testing: The battery should be tested with a hydrometer and kept to a specific gravity of 1.250 or above. Always test a battery for state of charge before adding water. A dangerously low point of charge is indicated by a hydrometer reading of 1.150 which will permit the battery to freeze at temperatures only a few degrees below the freezing point of water. A specific gravity of 1.250 will permit the battery to withstand temperatures as low as -60°F. (-51°C.) without freezing.

When the specific gravity difference between cells of the battery exceeds .025, it indicates the battery may soon need replacing.

Water Addition: The electrolyte level should be maintained 3/8 inch (9.5 mm.) above the top of the separators or insulators by addition of distilled water or "approved water" (water free from impurities by analysis). Do not overfill or underfill the cells of the battery as either has a detrimental effect on battery life.

Charging: The charging rate is correct when the battery maintains a minimum specific gravity of 1.250 and does not require the addition of more than 1 ounce of water per cell per week or 50 service hours.

When there is evidence of either overcharging or undercharging, the cause should be found and corrected as soon as possible to protect the service life of the battery. See the topics, CHARGING ALTERNATOR and WIRING.

Cleanliness: Keep the top of the battery clean and dry to prevent current losses and keep the terminals clean and tight. To clean corrosion from the battery terminals, scrub them with a weak solution of bicarbonate of soda (baking soda) and water. Dry the battery thoroughly, then coat the terminals with lubricant to prevent corrosion. Keep the battery securely fastened in its compartment at all times.

Installation: When replacing a battery that has been removed, make certain the cables are attached to the correct battery terminals. Improper connections may damage the electrical system.

Charging Alternator (24 and 12 Volt Systems)

The charging alternator is designed to give long service periods with a minimum amount of maintenance. The grease reservoirs, for each of the two ball bearings on which the rotor is mounted, eliminate the need for frequent bearing lubrication. Six rectifier diodes act to change A.C. power to D.C. power which appears at the D.C. output terminal on the alternator.


Alternator Removal: Remove the wires from the alternator. Remove the bolts or stud nuts that hold the alternator in position and lift it off the engine.

Alternator Installation: Disconnect the battery before installing the alternator. Install the alternator on the engine. Use extreme care in correctly connecting the wires to the alternator. Connect the wire from the battery to the large terminal and the ground wire to the small terminal on the alternator. Install the drive belts and adjust belt tension. See the topic, CHARGING ALTERNATOR AND WATER PUMP DRIVE BELTS.

Use extreme care in connecting the battery. The output terminal of the alternator is positive (+) and should be connected to the positive (+) terminal of the battery. The output terminal of the alternator is always positive (+).


Do not attempt to polarize a charging alternator. If improper connections are made, the rectifiers in the alternator and the transistors in the regulator portion of the alternator may be damaged.

Alternator Regulator: A transistor type regulator is incorporated in the alternator and is adjusted at the factory for average operating conditions. The voltage output may have to be readjusted to provide the proper charging rate for the particular operating conditions of the machine. In case of failure, the alternator should be taken to your AVSpare dealer, where the output of the alternator can be checked and regulated accordingly.

Charging Rate: The regulator in the alternator automatically adjusts the charging rate by sensing the electrical system voltage. As the battery becomes fully charged, voltage rises and the charging rate should drop until the ammeter indicates a rate only perceptibly above zero.

When improper charging of the battery is encountered, the entire electrical system should be carefully checked. Loose or dirty connections, worn or broken wires can prevent a good alternator from functioning properly. See the topics, BATTERY and CHARGING ALTERNATOR.


When recharging the battery or using booster batteries from an external source, disconnect the battery from the alternator to prevent damage to rectifiers in the alternator.


The wiring forms an important part of the electrical system and care should be used to protect it from damage. When the electrical system is being serviced, check the wiring for loose or dirty connections, worn insulation or broken wires. Inspect the battery terminals and cables. Poor connections or wiring can cause trouble or damage in other parts of the electrical system. See the topic, BATTERY, CHARGING ALTERNATOR.

Wiring Diagram: The diagram is furnished so that when it becomes necessary to disturb the electrical equipment for purposes of reconditioning or parts replacement, reassembling may be accomplished without difficulty.



Circuit Breaker: A circuit breaker located in the gauge panel is to break the flow of current from the battery, whenever there is an excessive load or a grounded wire in the circuit. If the flow of current from the battery has been shut off, the wiring should be checked. To reset the circuit breaker, push in the reset button.