1. Verify Power IN to Distributor:
* Precise Location: You say you have power *going into* the distributor. Be absolutely certain you're checking the correct wire(s) at the correct point. The distributor receives power from the ignition switch via the ignition coil. Use a test light or multimeter to confirm power is present at the coil's + terminal (usually the one connected to the ignition switch) *when* the key is in the "ON" or "START" position. If power isn't getting to the coil, the problem is *before* the distributor.
2. Check the Distributor Itself:
* Internal Wiring: The distributor's internal wiring can be the culprit. A damaged wire inside the distributor cap or rotor can prevent the spark from reaching the spark plug wires. Inspect these parts carefully for any cracks or damage. Replace these components as a precaution even if they look fine; they are inexpensive and a common cause of this issue.
* Distributor Shaft: The distributor shaft could be worn or damaged, preventing proper rotation and interrupting the signal to the pickup coil. This is more difficult to check without specialized tools but is a possibility.
* Capacitor (Condenser): A faulty condenser (capacitor) can cause weak sparks or prevent them altogether. This is relatively inexpensive to replace and is often a candidate in these scenarios.
3. Wiring Between Distributor and Ignition Coil:
* Continuity Test: Use a multimeter to test the continuity of the wires running from the distributor to the ignition coil. Any breaks or shorts in these wires will prevent the spark.
* Connections: Ensure all wire connections are clean, secure, and properly seated. Corrosion can disrupt electrical flow.
4. Ignition Control Module (ICM): (Depending on the year and specific engine) Some 85 C10s have an ICM (Ignition Control Module). This module controls the ignition system and could be faulty. Check your wiring diagram to see if your truck has one. It’s usually found near the distributor.
5. Test for Spark:
* Direct Spark Test: To pinpoint the issue, pull one spark plug wire from a spark plug. Ground the end of the spark plug wire (be careful, it might have a sharp edge!) to the engine block. Then have someone crank the engine while you observe the spark plug wire. If you see a strong blue spark, the problem is likely in the plug wire, spark plug, or a connection issue on the spark plug. If no spark, the problem is definitely in the distributor or upstream from it.
6. Professional Help: If you've gone through all these steps and still can't find the issue, it's best to take your truck to a qualified mechanic. Diagnosing electrical problems can be challenging, and a mechanic may have specialized tools and experience that can help identify the root cause more quickly.
Remember to disconnect the negative battery terminal before working on any electrical components. Always consult a wiring diagram specific to your 1985 Chevy C10 model to ensure you're working on the correct components and wires.
