Most Likely Culprits:
* Alternator: A failing alternator can sometimes create a "pop" sound (due to internal failure) and then fail to properly charge the battery. With a weak or dead battery, your lights may dim or go out completely. The turn signals might still work because they draw less power. This is a prime suspect given the sudden failure.
* Wiring Harness: A short circuit or a damaged wire in the main power harness could have caused the "pop" (the sound of the short) and cut off power to the lights. This could be anywhere from the battery to the light switches. Finding this will require visual inspection of the harness. Look for areas that have been rubbed or damaged, especially near the engine compartment and firewall. This is difficult to diagnose without tracing wires.
* Ignition Switch: Although less likely, a faulty ignition switch could be cutting power to certain circuits. This is often linked to other electrical issues, and a bad ignition switch can lead to more than just lighting problems.
* Light Switch: While less probable given all lights failing at once, a complete failure of the light switch could happen and cause this. It might be seized in the "off" position internally.
Troubleshooting Steps:
1. Battery Voltage Check: Use a voltmeter to check the battery voltage. It should be around 12.6V when the engine is off and ideally above 13.5V when the engine is running. Low voltage points to a charging system problem (alternator or battery).
2. Alternator Test: A simple alternator test involves checking the voltage while the engine is running. If it remains low, even after the battery is charged, the alternator is likely the culprit. A proper alternator test may require specialized tools.
3. Visual Inspection: Carefully examine all wiring related to the lights. Look for:
* Burned wires: Look for evidence of melting or discoloration.
* Loose connections: Check all connectors and ensure they are securely attached. Pay close attention to the main power feed from the battery.
* Damaged insulation: Look for exposed wires or frayed insulation that might be shorting to ground.
4. Test the Light Switch: This is a more involved step. If you have access to a wiring diagram, try checking the switch's continuity and power in different positions using a multimeter.
5. Fuse Check (again, with more scrutiny): Make absolutely sure you've checked ALL fuses, even those that might seem unrelated to lighting. Sometimes a blown fuse will cause cascading failures. Look carefully for any that might be showing signs of damage (bulging, discoloration).
6. Relay Check: There might be relays related to the lighting system. If you find them, you can swap them with other relays of the same amperage rating to see if the problem changes location.
Important Considerations:
* Safety: Working with car electrical systems can be dangerous. Disconnect the negative battery terminal before working on any wiring to prevent accidental shorts.
* Wiring Diagram: A wiring diagram specific to your 1989 Jeep Cherokee is invaluable. You can often find these online through Jeep forums or repair manuals. This diagram will show you the path of the wires and help you isolate the problem.
If you're not comfortable with electrical work, it's best to take your Jeep to a qualified mechanic. A faulty alternator is a relatively common and easy fix, but a faulty wiring harness can be complex to troubleshoot.
