Usage:
914G (7ZM, 9WM),
928G (6XR, 7SR) Wheel Loaders IT14G (8ZM, 1WN),
IT28G (8CR, 9AR) Integrated Toolcarriers
Reference: Service Manual Module, SENR6777: 914G Wheel Loader And IT14G Integrated Toolcarrier Electrical System Schematic. This module is part of Service Manual SENR6760, 914G Wheel Loader & IT14G Integrated Toolcarrier.
Reference: Service Manual Module, SENR1229; 928G Wheel Loader And IT28G Integrated Toolcarrier Electrical System Schematic. This module is part of Service Manual SENR1215, 929G Wheel Loader & IT28G Integrated Toolcarrier.
Reference: Service Magazine, SEPD1242; November 8, 1982; Page 7; "Do Not Center-Tap Batteries In 24-Volt System To Operate 12-Volt Accessories."
Reference: Service Magazine, SEBD1551; January 21, 1985; Page 1; "Correct Use of 9G6981 Converter Assembly."
The small wheel loaders listed above have the capability of powering various electrical devices for the convenience of the user. Unused (spare) terminals are provided on the fuse blocks to allow the addition of one or more electrical circuits.
Before an electrical circuit can be added, the voltage and current (amperage) requirements for the new electrical device must be determined. These values are typically provided by the manufacturer of the electrical device. In addition, the conditions for providing power to the electrical device must also be determined. These three elements will dictate where and how the new wiring connections must be made.
Voltage Requirements
Most Caterpillar machines have a 24 volt (nominal) electrical system. This is provided through the use of two 12 volt batteries, which are connected in series.
Although it is possible to power a 12 volt electrical device by center-tapping the batteries, this practice is discouraged because of the high risk of personal injury and equipment damage that could result. Also, center-tapping will result in uneven battery charging and early battery failure. 24 volt to 12 volt Voltage Converters are available for installation on wheel loaders when there is a need for a safe and reliable 12 volt power source.
Current (Amperage) Rating
The current rating of an electrical device is the maximum amount of current (with respect to time) that can flow through the device without damage to the device. The current rating of the electrical circuit must match the current rating of the device. Depending on the current rating of the electrical device, the current rating of the electrical circuit can be 10 amps, 15 amps, or 20 amps. The desired current rating of the electrical circuit will determine the wire size (gauge) and the terminal size required.
NOTE: Do not connect any electrical device directly to the battery or to any other power source without a fuse or a circuit breaker in the circuit between the electrical device and the power source.
Switched Power or Unswitched Power
"Unswitched" and "Switched" are electrical terms that indicate when power is being supplied in an electrical circuit. "Unswitched" indicates that power is available in an electrical circuit any time the contacts of a main power switch or circuit breaker are closed.
"Switched" indicates that power in an electrical circuit depends on the electrical status of a switching device, such as a key switch, that is downstream of the main power switch or circuit breaker. Power is available when the contacts of a main power switch or circuit breaker are closed and the switching device is in the ON position.
The need for "Unswitched" or "Switched" power will determine where a new electrical circuit will be connected in the electrical system.
Adding A New Electrical Circuit
Illustration 1.
Front View of Relay/Fuse and Fuse Blocks - 914G and IT14G Machines.
Illustration 2.
Front View of Fuse Blocks - 928G and IT28G Machines.
After the power, current, and condition requirements are known, the next step is to determine where to make the connections in the electrical system and what materials are required to establish the new electrical circuit. Charts 1-4 provide a guide for identifying the power source, the available spare terminal positions, and the electrical components, based on circuit size (amperage) needed to install a new electrical circuit.
The procedure for adding a new electrical circuit is provided below. See Illustrations 1 and 2.
1. Open the main power disconnect or circuit breaker to de-energize the machine's electrical systems.
2. Remove the cover plate from the electrical compartment that contains the electrical relays and the fuses. This compartment is located just inside the right side door of the cab.
3. Remove the relay and fuse blocks. Load the new blade terminal and wire assembly into the desired relay/fuse block position. Follow the procedure, "Loading New Terminal in Terminal Block," that is provided in this article.
4. Re-mount the relay and fuse blocks inside the electrical compartment.
5. Route the wire from the new blade terminal and wire assembly to the new electrical device. This is the positive power lead for the new electrical device.
NOTE: Ensure that the new electrical device is properly grounded according to the manufacturer's instructions. If necessary, install a new ground wire from the electrical device to the cab ground which is located under the cab floor on the right side of the machine.
6. Install the proper fuse in the selected location.
NOTE: Use Charts 1-4, as appropriate, to determine the size of fuse needed (Column G).
7. Replace the cover on the electrical compartment.
8. Energize the new electrical circuit by closing the main power disconnect or circuit breaker and, if applicable, turning the switching device (key switch) to the ON position.
9. Check the new electrical device for proper operation.
Loading New Terminal in Terminal Block
1. Remove the two Torx screws (1) in order to remove the relay/fuse blocks and base (2) from its mounted position. See Illustrations 1 and 2.
2. Disconnect fuse bus bar terminals from the Main Power Relay and the Lamp Breaker.
3. Withdraw the relay/fuse blocks and base from inside the electrical compartment in order to gain access to the back side of the base. See Illustrations 1 and 2, Detail A.
4. Remove all three relay/fuse blocks from the base by using a small screwdriver to release the four tangs that secure each relay/fuse block. Access the tangs from the back of the base. See Illustrations 1 and 2, Detail B.
5. Select the relay/fuse block to which the new circuit will be added. Use a small screwdriver to remove the blue terminal locking tab from the selected relay/fuse block.
NOTE: Use Charts 1-4, as appropriate, to identify power source (Column A) and spare terminal locations (Column B).
6. Install the blade terminal on a length of electrical wire. The length of electrical wire can be determined by loosely routing the wire from inside the electrical compartment to the mounting location of the new electrical device.
NOTE: Use Charts 1-4, as appropriate, to determine the proper wire size (Column C, Column D, and Column E) and the proper blade terminal (Column F).
7. Load the assembled blade terminal and wire in the desired spare terminal position (as determined in Step 6).
8. Reinstall the blue terminal locking tab.
9. Reinstall the three relay/fuse blocks on the base (2).
10. Reconnect the fuse bus bar terminals for the Main Power Relay and the Lamp Breaker.
11. Position the reassembled relay/fuse blocks and base inside the electrical compartment.
12. Remount the reassembled fuse blocks and base with the two Torx screws.