1. Verify Headlight Bulbs:
* Obvious but crucial: Even though you've focused on fuses and the switch, make absolutely sure the low beam bulbs themselves aren't burnt out. They're easy to check and replace. Sometimes a bulb can appear fine but be internally broken.
2. Wiring Harness Inspection:
* Low Beam Circuit: Locate the wiring harness leading from the headlight switch to the low beam headlights. This is likely a complex harness, and tracing it requires patience. Look for:
* Broken wires: Carefully inspect the wires for any breaks, frays, or corrosion, especially near connectors and where the harness bends. Look particularly carefully near the firewall and where the harness enters the engine compartment.
* Loose connections: Check all connectors along the low beam circuit for secure connections. Wiggle them gently while someone tests the headlights – a flickering light suggests a loose connection.
* Corrosion: Clean any corrosion you find with a wire brush and electrical contact cleaner.
* Grounds: A poor ground can cause all sorts of electrical gremlins. Check the ground points for both headlights. These are usually metal points bolted to the chassis. Clean them thoroughly.
3. Headlight Switch (Again):
* Internal Failure: Even a new headlight switch can be faulty. While unlikely if brand new, it's possible the replacement is defective.
* Incorrect Installation: Double-check that the new switch is installed correctly. A wiring diagram for your specific van's year is extremely helpful here.
4. Multi-Function Switch:
* Integrated Circuitry: The multi-function switch often controls several things including turn signals, wipers, and sometimes parts of the lighting. A faulty internal component could be disrupting the low beam circuit without affecting the high beams. This requires removing and inspecting, or replacing, the switch.
5. Relay (If Applicable):
* Check the relay: Some vehicles use a relay for the low beam circuit. If your G20 does (consult a wiring diagram), check it for continuity using a multimeter. A simple swap with a known good relay is a quick test.
6. Wiring Diagram:
* Essential Tool: A wiring diagram specific to your 1994 Chevy G-20 van is absolutely essential. You can often find these online (search for "1994 Chevy G20 wiring diagram") or at a parts store. This diagram will show the exact path of the low beam circuit, allowing you to pinpoint the problem area efficiently.
7. Professional Help:
* Last Resort: If you've checked all of the above and still can't find the problem, it's time to consult a qualified auto electrician. They have specialized tools and expertise to diagnose more complex electrical issues.
Safety Precautions:
* Disconnect the battery's negative terminal before working on any part of the vehicle's electrical system. This prevents accidental shorts and shocks.
* Never work under the vehicle without safety stands.
By systematically checking each component and using a wiring diagram, you should be able to isolate the cause of the low beam failure. Remember that patience and methodical troubleshooting are key to success.
