1. Visual Inspection:
* Motor: Start by visually inspecting the wiper motor itself. Look for any obvious signs of damage, such as corrosion, loose connections, or broken mounting brackets. The motor is usually located under the dash or cowl (the area where the windshield meets the body). You might need to remove some trim panels to access it fully. Look for anything obviously burned or melted.
* Linkage: Examine the linkage connecting the motor to the wiper arms. Check for broken or bent parts, loose connections, or binding. Wiggle the arms to check for free movement. Sometimes the linkage gets seized with age and corrosion.
* Wiring: Inspect the wiring harness connected to the motor for any damaged, frayed, or disconnected wires. Pay close attention to the connectors.
2. Testing the Motor (Directly):
This is the most definitive test but requires caution. Disconnect the negative battery cable before starting any electrical work.
* Locate the Motor Connector: Find the electrical connector going to the wiper motor.
* Apply 12V Directly (Caution!): Using jumper wires and a 12V power source (like a battery charger set to a low amperage), carefully apply 12V to the motor's terminals. You MUST know which wire is positive and which is negative. Incorrect polarity can damage the motor. Consult a wiring diagram if unsure. The direction of the motor rotation will depend on how you connect the wires.
* Observe the Motor: If the motor runs, the motor itself is likely good. If it doesn't, the motor is faulty. If it runs but in the wrong direction, you may have a reversed wiring condition.
* IMPORTANT: Only apply power for a few seconds at a time to avoid overheating the motor.
3. Testing the Switch:
If the motor runs directly, the problem lies elsewhere – likely the switch or wiring. Checking the switch is more complex. You could:
* Use a Multimeter: With the ignition on, you can use a multimeter to check for continuity and voltage at the switch's terminals. You'll need a wiring diagram to identify which terminals correspond to the motor. This step is advanced and requires electrical knowledge.
* Bypass the Switch (With Caution!): As a last resort (and only if you understand the risks), you could temporarily bypass the switch by connecting the wires that normally go to the switch directly to the power source. This is generally not recommended as it could cause damage if done improperly and could result in wipers running constantly.
4. Checking the Wiring:
* Continuity Test: Use a multimeter to test the continuity of the wires from the switch to the motor. A break in the circuit would prevent the wipers from working.
* Voltage Drop Test: Check the voltage at both ends of the wires. A significant voltage drop indicates a problem within the wiring harness itself (high resistance).
5. Fuse Check:
Check the fuse associated with the windshield wiper motor. A blown fuse is a relatively easy fix. Consult your El Camino's owner's manual or a wiring diagram to find the correct fuse.
Important Considerations:
* Wiring Diagram: A wiring diagram specific to your 1977 El Camino is crucial for accurate testing. You can often find these online through classic car forums or repair manuals.
* Safety First: Always disconnect the negative battery cable before working on any electrical components.
* Professional Help: If you're not comfortable working with car electrical systems, it's best to take your El Camino to a qualified mechanic.
Remember, this is a general guide. The specific location of the motor and the wiring configuration might vary slightly depending on your El Camino's trim level. Always consult a repair manual or wiring diagram for precise instructions relevant to your vehicle.
