1. Headlight Motor itself:
* Binding: The motor might be binding due to age, corrosion, or lack of lubrication. Try gently moving the headlight assemblies by hand (with the car OFF and the ignition off!) to see if they move freely. Stiffness or resistance indicates a problem.
* Worn Gears: The internal gears of the motor can wear down over time, leading to inconsistent or jerky movement. This often requires motor replacement.
* Motor Failure: The motor itself might have simply burned out. This is a common issue with age.
2. Headlight Motor Switch:
* Switch Malfunction: The switch that controls the headlight motors can fail, sending incorrect signals or no signal at all.
* Wiring to the Switch: Check the wiring harness connection to the switch for corrosion, loose connections, or broken wires.
3. Linkage:
* Broken or Disconnected Linkage: The linkage that connects the motor to the headlights can break or become disconnected. Inspect the linkage rods and connections carefully. Look for bends, breaks, or loose bolts.
4. Vacuum System (if applicable):
While less common on 1981 models, *some* C3 Corvettes (depending on options) might have a vacuum-operated system supplementing or controlling the headlight motors. If this is the case, check for:
* Vacuum Leaks: Inspect the vacuum lines for cracks, holes, or loose connections. A leak will severely impact the system's ability to function correctly.
* Vacuum Pump (if equipped): Ensure the vacuum pump is functioning properly if one is part of your system.
5. Electrical System:
* Power Supply to the Motor: Check the power supply to the headlight motor using a multimeter. Make sure it's receiving the correct voltage.
* Fuses and Relays: Check the fuses and relays associated with the headlight motors in the fuse box.
Troubleshooting Steps:
1. Visual Inspection: Start with a thorough visual inspection of the headlight motors, linkage, wiring, and vacuum lines (if applicable). Look for obvious signs of damage or wear.
2. Test the Switch: Try manually moving the headlight switch to see if it responds consistently.
3. Check Wiring: Inspect all wiring connections for corrosion or damage.
4. Use a Multimeter: Use a multimeter to check for voltage at the motor and at the switch.
5. Test the Motor (with caution): If you're comfortable with basic electrical work, you can try applying direct power to the motor (with the ignition OFF and battery disconnected). This will tell you if the motor itself is faulty. Be extremely careful when doing this; incorrect wiring can damage the motor or even injure you.
If you're not comfortable working on the electrical system of your car, it's best to take it to a qualified mechanic. Replacing the headlight motor is a relatively common repair for older Corvettes, and a mechanic can diagnose and repair the issue efficiently. Also, a Corvette-specific shop will be very familiar with this issue.
