1. Bulbs:
* Burned out bulbs: This is the most common cause. Check all four turn signal bulbs (front and rear on both sides). Also check the hazard light bulbs. If a bulb is burnt out, replace it with the correct wattage.
2. Fuses:
* Blown fuse: Your truck likely has a fuse specifically for the turn signals. Consult your owner's manual to locate the fuse box and identify the correct fuse. Replace any blown fuses with the correct amperage rating.
3. Flasher Unit:
* Faulty flasher unit: This is a small electronic or electromechanical device that controls the blinking rate of the turn signals. It's usually located under the dash or in the fuse box. A bad flasher will result in no flash, a very fast flash, or a slow flash. Replacement is relatively inexpensive and easy. There are two common types: electronic and thermal. Make sure to get the right kind for your truck.
4. Wiring:
* Broken or corroded wires: Examine the wiring harness leading to and from the flasher unit, the turn signal switch, and the lights themselves. Look for broken wires, corrosion, or loose connections. Pay close attention to connections at the bulb sockets and the turn signal switch. A visual inspection is often insufficient; you may need a multimeter to test continuity.
* Short circuit: A short in the wiring can prevent the signals from working. This often requires tracing the wiring system to find the location of the short.
5. Turn Signal Switch:
* Faulty turn signal switch: The switch itself might be malfunctioning, preventing the signal from being sent to the flasher and bulbs. This is more involved to diagnose and might require testing with a multimeter. Sometimes cleaning the switch contacts can resolve the problem.
6. Multi-Function Switch (if equipped):
* Faulty multi-function switch: Some vehicles combine turn signals, wipers, and headlights into one switch. A problem in the switch could affect the turn signals.
7. Grounding Issues:
* Poor ground connection: A poor ground connection can interrupt the electrical flow, preventing the signals from functioning correctly. Check the ground points related to the lighting system.
Troubleshooting Steps:
1. Start with the easiest: Check the bulbs and fuses first.
2. Visual Inspection: Carefully inspect the wiring harness for any obvious damage.
3. Test the Flasher: If the bulbs and fuses are good, the flasher unit is a likely suspect. Try swapping it with a known good one (if you have access to one).
4. Use a Multimeter: If you have a multimeter, you can test the voltage at various points in the circuit to pinpoint the problem area. This is essential for diagnosing wiring issues and switch problems.
5. Consult a Wiring Diagram: A wiring diagram for your specific 1970 Chevy truck model will be invaluable in tracing the electrical paths. These are often available online.
If you're not comfortable working with automotive electrical systems, it's best to take your truck to a qualified mechanic. Improperly diagnosing and repairing electrical problems can lead to further damage.
