1. Fuses: This is the most common and easiest thing to check. Your owner's manual will show you the fuse box location and diagram. Look for fuses related to headlights (they're usually clearly labeled). Check for blown fuses (a broken filament inside). Replace any blown fuses with the correct amperage. If the new fuse blows immediately after replacement, you have a short circuit – don't keep replacing it!
2. Headlight Switch: The headlight switch itself could be faulty. It's possible it's broken internally, preventing the circuit from closing. Testing this requires more advanced electrical knowledge or a multimeter.
3. Headlight Relay (if equipped): Some 1984 Cadillacs might use a relay for the headlights. A bad relay can prevent power from reaching the headlights. You can try swapping the relay with a known good one of the same type (check the markings on the relay).
4. Wiring: This is the most difficult to diagnose. Look for broken or corroded wires, especially in the areas where the wiring harness is likely to flex (around the steering column, engine bay, and near the headlights themselves). A visual inspection is necessary, but a multimeter might be needed to trace the circuit.
5. Bulbs: Check the headlight bulbs themselves. They may simply be burned out. This is easy to check and replace. Ensure you use the correct type of bulb as specified in your owner's manual.
6. Dimming Switch (if equipped): Some cars have a dimming switch that might be stuck in the "off" position. Try manipulating this if your car has one.
7. Multifunction Switch (Turn Signal/Wiper Switch): In some vehicles, this switch also controls the headlights. A faulty multifunction switch could prevent the headlights from activating.
8. Battery: A weak or dead battery can sometimes prevent certain electrical components, including headlights, from working. Check the battery voltage with a multimeter.
Troubleshooting Steps:
1. Start with the fuses. This is the quickest and easiest check.
2. Check the bulbs. It's a simple check that could solve the problem.
3. Visually inspect the wiring. Look for obvious damage.
4. If you're comfortable with it, check the relay (if equipped).
5. Test the headlight switch and related circuits with a multimeter. (This requires some electrical knowledge).
6. Consider the battery and the dimming switch/multifunction switch.
If you are not comfortable working with car electrical systems, it's best to take your Cadillac to a qualified mechanic. Trying to diagnose electrical issues without proper knowledge can lead to further damage. A proper diagnostic tool may also be required to check for various sensor issues that might be contributing to this problem.
