* Under the hood: Often mounted on the inner fender well, near the firewall. Look for a somewhat rectangular black box with many wiring harnesses connected to it.
* Under the dash: Less common in that year, but possible depending on the truck's configuration.
Before assuming the ECM is the problem: While a faulty ECM *could* cause a no-fire condition, it's less likely than other components. The fact that you've tried "everything else" suggests you've already checked some key areas. To be certain the ECM is the culprit, a proper diagnostic procedure is necessary. Jumping straight to replacing it is expensive and often unnecessary.
Here's a more logical troubleshooting approach if you have no spark:
1. Battery and Connections: Ensure the battery is fully charged and the terminals are clean and tight. A weak battery can cause intermittent or no spark.
2. Ignition Switch: Verify the ignition switch is functioning correctly. Does it turn on accessories and the fuel pump when the key is turned to the "on" position?
3. Ignition Coil: Test the coil for proper resistance and spark output using a multimeter and a spark tester. This is a common culprit.
4. Distributor Cap and Rotor: Inspect the distributor cap and rotor for cracks, carbon tracking, or corrosion. These components can prevent the spark from reaching the spark plugs.
5. Spark Plugs and Wires: Check the spark plugs for proper gap and condition. Replace worn or fouled plugs. Inspect the spark plug wires for cracks or damage.
6. Cranking System: A weak starter motor may not crank the engine fast enough to generate a spark.
7. Ignition Module (if separate from ECM): Some 1983 C-10s had a separate ignition module. It's often near the coil or distributor. This requires testing as well.
8. Fuel Pump: Although you're focused on spark, ensure the fuel pump is operating and delivering fuel to the carburetor or fuel injectors. No fuel will also result in a no-start situation.
9. Distributor: The distributor itself can malfunction. This is more involved and often requires professional help to check the mechanical and electrical aspects.
Only after thoroughly checking all these should you suspect the ECM. Even then, a diagnostic scan tool or professional diagnosis is highly recommended to confirm. Replacing the ECM is an expensive gamble without proper testing.
