The 1990 Peterbilt 379 is a classic truck that many people still enjoy driving today. However, as these trucks age, the wiring can become problematic. In this article, we will provide a wiring diagram for the 1990 Peterbilt 379, along with some tips and frequently asked questions that will help you troubleshoot any wiring issues you may encounter.
The Wiring Diagram
The wiring diagram for the 1990 Peterbilt 379 is a comprehensive diagram that illustrates the wiring connections for the entire truck. This diagram is very helpful in troubleshooting any wiring issues you may be experiencing.
Here is a breakdown of the different components of the wiring diagram:
| Component | Description |
|---|---|
| Battery | Provides power to the entire truck |
| Alternator | Charges the battery while the engine is running |
| Starter | Engages the engine to start |
| Ignition Switch | Activates the electrical system when the key is turned |
| Lighting System | Controls all the lights on the truck |
| Heating and Air Conditioning | Controls the heating and air conditioning system on the truck |
| Instrument Cluster | Displays the truck’s speed, RPM, fuel level, and other important information |
| Radio | Provides entertainment and communication for the driver and passengers |
| Trailer Connector | Connects the truck to a trailer |
Battery
The battery is the most important component of the electrical system on the 1990 Peterbilt 379. Without a properly functioning battery, the truck will not start. If you are experiencing issues with the battery, it is important to check the connections to ensure they are clean and tight.
If you have checked the connections and the battery is still not working properly, you may need to replace it. You should also check the alternator to ensure it is charging the battery properly.
Alternator
The alternator is responsible for charging the battery while the engine is running. If the alternator is not working properly, the battery will not be charged, and the truck may not start. The first step in troubleshooting the alternator is to check the connections to ensure they are clean and tight.
If the connections are fine, you may need to replace the alternator. You should also check the voltage output of the alternator to ensure it is working properly. If the voltage is too high or too low, the alternator may need to be replaced.
Starter
The starter is responsible for engaging the engine to start. If the starter is not working properly, the engine will not start. The first step in troubleshooting the starter is to check the connections to ensure they are clean and tight.
If the connections are fine, you may need to replace the starter. You should also check the battery to ensure it is fully charged, as a weak battery can cause the starter to fail.
Ignition Switch
The ignition switch is responsible for activating the electrical system when the key is turned. If the ignition switch is not working properly, the truck will not start. The first step in troubleshooting the ignition switch is to check the connections to ensure they are clean and tight.
If the connections are fine, you may need to replace the ignition switch. It is important to ensure that the replacement switch is compatible with the 1990 Peterbilt 379.
Lighting System
The lighting system controls all the lights on the truck, including headlights, taillights, and turn signals. If any of the lights are not working properly, it is important to check the connections to ensure they are clean and tight.
If the connections are fine, you may need to replace the bulbs or the entire lighting unit. It is important to ensure that the replacement parts are compatible with the 1990 Peterbilt 379.
Heating and Air Conditioning
The heating and air conditioning system controls the temperature inside the truck. If the system is not working properly, it may indicate a problem with the wiring or the components of the system. The first step in troubleshooting the system is to check the connections to ensure they are clean and tight.
If the connections are fine, you may need to replace the components of the system, such as the blower motor or the compressor. It is important to ensure that the replacement parts are compatible with the 1990 Peterbilt 379.
Instrument Cluster
The instrument cluster displays the truck’s speed, RPM, fuel level, and other important information. If the instrument cluster is not working properly, it may indicate a problem with the wiring or the components of the system. The first step in troubleshooting the system is to check the connections to ensure they are clean and tight.
If the connections are fine, you may need to replace the components of the cluster, such as the speedometer or the fuel gauge. It is important to ensure that the replacement parts are compatible with the 1990 Peterbilt 379.
Radio
The radio provides entertainment and communication for the driver and passengers. If the radio is not working properly, it may indicate a problem with the wiring or the components of the system. The first step in troubleshooting the system is to check the connections to ensure they are clean and tight.
If the connections are fine, you may need to replace the radio or the speakers. It is important to ensure that the replacement parts are compatible with the 1990 Peterbilt 379.
Trailer Connector
The trailer connector connects the truck to a trailer. If the connector is not working properly, it may indicate a problem with the wiring or the connector itself. The first step in troubleshooting the system is to check the connections to ensure they are clean and tight.
If the connections are fine, you may need to replace the connector. It is important to ensure that the replacement connector is compatible with the 1990 Peterbilt 379 and meets all safety standards.
Frequently Asked Questions
What Should I Do If My Truck Won’t Start?
If your truck won’t start, the first step is to check the battery and the connections to ensure they are clean and tight. If the battery and connections are fine, you may need to check the alternator, starter, and ignition switch. If you are unable to troubleshoot the issue, it is best to take the truck to a mechanic for a professional diagnosis.
How Do I Replace a Blown Fuse?
To replace a blown fuse, locate the fuse box and identify the fuse that needs to be replaced. Use a fuse puller or pliers to remove the old fuse and replace it with a new fuse of the same amperage rating. Always use the correct amperage rating to avoid damaging the electrical system.
Why Are My Lights Flickering?
If your lights are flickering, it may indicate a problem with the alternator, voltage regulator, or wiring. Take the truck to a mechanic for a professional diagnosis.
How Do I Test the Voltage Output of the Alternator?
To test the voltage output of the alternator, use a multimeter to measure the voltage at the battery terminals while the engine is running. The voltage should be between 13.8 and 14.4 volts. If the voltage is outside this range, the alternator may need to be replaced.
Can I Use a Different Type of Battery?
It is best to use the recommended type of battery for your 1990 Peterbilt 379. Using a different type of battery may cause compatibility issues and can potentially damage the electrical system.
Conclusion
The wiring diagram for the 1990 Peterbilt 379 is a helpful tool for troubleshooting any wiring issues you may encounter. By following the tips and frequently asked questions in this article, you can ensure that your truck’s electrical system is functioning properly.
