Possible Causes:
* Faulty Dimmer Switch: The most likely culprit. The switch itself may be internally shorted or have a bad connection, allowing a small amount of current to constantly flow even when turned off.
* Short Circuit in the Wiring: A short in the wiring harness could be causing a partial ground, resulting in a constant low-level current feeding the lights. This short could be anywhere between the dimmer switch and the lights themselves. Moisture or damage to the wiring loom is a common cause.
* Faulty Light Bulbs: While less likely to cause *dim* lights that stay on, a bulb with a very low internal resistance could draw a small current continuously. Check all bulbs to eliminate this possibility.
* Problem with the Ground: A poor ground connection somewhere in the circuit could also lead to the lights staying partially on.
* Faulty Grounding within the Dimmer Switch Assembly: The dimmer switch may not be grounding properly, resulting in the partial power issue.
Troubleshooting Steps:
1. Check the Bulbs: Start by examining all the interior lights. If one is burned out oddly, replace it (or all of them to eliminate this possibility).
2. Test the Dimmer Switch: This is best done with a multimeter. With the switch turned off, you should read very close to zero ohms (total break in the circuit) between the power input and the light output terminals. If you get a low resistance reading, the switch is faulty. Note that some switches don't have a true "off" position and may have a very high resistance instead of an infinite one, but this will often be significantly higher than your current reading.
3. Inspect the Wiring: Carefully inspect the wiring harness for any signs of damage, fraying, or corrosion, particularly around the dimmer switch and the light fixtures. Look for areas where wires might be touching metal parts of the car. This is the most difficult step and might require some disassembly.
4. Check the Ground Connections: Find the ground points for the interior lighting circuit and make sure they are clean and secure. Use a wire brush to clean any corrosion and re-tighten the connections.
5. Test Voltage: With a multimeter, measure the voltage at the lights themselves, both with the switch on and off. A small voltage present even with the switch off strongly suggests a short.
Important Considerations:
* Safety First: Always disconnect the battery's negative terminal before working on any electrical system in your car. This prevents accidental shorts and shocks.
* Wiring Diagrams: A 1987 Corvette wiring diagram will be invaluable. You can find these online through Corvette forums or repair manuals.
* Professional Help: If you're not comfortable working with car electronics, it's best to take your Corvette to a qualified mechanic or electrician. Electrical faults can be tricky to diagnose and repair.
The dimmer switch is the most probable culprit, given the symptoms. Replacing it is usually a straightforward repair, but if the issue persists after replacing it, you’ll need to investigate the wiring more thoroughly.
