1. Fuses:
* Locate the fuse box: This is usually under the hood or inside the cab, often near the steering column or under the dash. Your owner's manual will show the exact location and a fuse diagram.
* Check the relevant fuses: Look for fuses labeled "headlights," "taillights," "running lights," or similar. Also check any fuses marked as "ignition" or related to the lighting circuit. Use a test light or multimeter to confirm if the fuse is blown (no continuity). Replace any blown fuses with fuses of the *correct amperage*. Using a higher amperage fuse is dangerous and could cause a fire.
2. Bulbs:
* Check all bulbs: Even if you suspect a wiring issue, examine all headlights (high and low beams) and taillights (including brake lights, reverse lights, and turn signals). A blown bulb in one location *could* sometimes cause a short that trips other circuits, though this is less likely than a wiring or fuse problem.
3. Wiring & Connections:
* Inspect the wiring harness: This is the most likely culprit. Carefully examine the wiring harnesses leading to the headlights and taillights for any signs of damage, corrosion, broken wires, or loose connections. Pay close attention to the connections at the back of the headlight and taillight assemblies, as well as any connectors along the wiring runs. Look for areas where wires might be rubbing against metal parts.
* Check the headlight switch: The headlight switch itself can fail, interrupting power to the entire lighting system. This requires some electrical testing (see below).
* Ground connections: A poor ground connection can cause widespread electrical problems. Make sure the ground wires connected to the chassis are clean and tight. These ground points are often near the headlights and taillights.
4. Multi-meter Testing:
If you're comfortable working with electricity, a multimeter is invaluable. You can test:
* Voltage at the fuse: With the headlights switched on, check the voltage *at the fuse terminals*. If there's no voltage, the problem is upstream (before the fuse). If there's voltage *at* the fuse but none beyond, the fuse is likely the problem (even if it looks okay).
* Voltage at the switch: With the headlights switched on, check the voltage at the headlight switch. You'll need to find the correct wires to probe.
* Voltage at the headlight and taillight connectors: With the headlights switched on, check the voltage at the connectors going to the headlights and taillights. If there's no voltage here, the problem is in the wiring between the switch and the lights.
* Continuity of wires: With the multimeter set to continuity (or ohms), test the continuity of the wires. This will help pinpoint breaks in the wiring.
5. Additional Considerations:
* Brake light switch: If the brake lights aren't working and you have other electrical problems, a failing brake light switch could be a potential contributor to other issues.
* Ignition switch: A faulty ignition switch could interrupt power to certain circuits, although this is less common if your other electricals are working.
* Wiring diagram: A wiring diagram for your 1980 Chevy Silverado is crucial for proper troubleshooting. You can often find these online through sites specializing in classic car parts or repair manuals.
Safety Precautions:
* Disconnect the battery's negative terminal before working on the electrical system.
* Never work on the electrical system with the engine running.
* Be careful not to short-circuit wires.
If you're not comfortable working with car electrical systems, it's best to take your truck to a qualified mechanic. The troubleshooting process can be quite involved, especially on older vehicles.
