* Instrument Cluster itself: The LCD display might be faulty internally, even if the ECM is good. There could be a broken trace on the circuit board, a bad connection, or a failed LCD element. This would require testing or replacement of the instrument cluster.
* Power and Ground Connections to the Instrument Cluster: Check all wiring harnesses and connectors going to the instrument cluster for corrosion, loose connections, broken wires, or poor grounds. A bad ground is a very common cause of electrical gremlins. Trace the wires back to their source.
* Fuse(s) or Circuit Breaker(s): Even though you've tackled the ECM, there might be separate fuses or circuit breakers dedicated to the instrument cluster and cooling fans. Check these carefully.
* Wiring Harness Problems: A break or short in the wiring harness supplying power and signals to the instrument cluster and fans could be the root cause. Inspect the harness thoroughly for damage.
* Ignition Switch: A failing ignition switch might not properly supply power to certain circuits, including the instrument cluster and fans.
* Body Control Module (BCM) – (if equipped): Some 1985 Corvettes might have a BCM which manages various functions. A malfunctioning BCM could affect both the instrument panel and fans. This is less likely given the ECM replacement but worth considering.
* Temperature Sensor(s): If the cooling fan issue is independent of the dash issue, a faulty coolant temperature sensor might be preventing the fans from activating, regardless of the dash display.
* Relay(s): Check the relays associated with the cooling fans. They're often a source of intermittent or complete failures.
Troubleshooting Steps:
1. Thorough visual inspection: Examine all wiring, connectors, and components related to the instrument cluster and cooling fans for any signs of damage.
2. Check fuses and circuit breakers: Replace any blown fuses, but be sure to replace them with the correct amperage.
3. Test for power and ground: Use a multimeter to check for proper voltage at the power and ground connections to the instrument cluster and the fan motor(s).
4. Test the relays: Swap the relays (if possible) with known good ones to see if that solves the problem.
5. Consult a wiring diagram: A wiring diagram for your specific 1985 Corvette is essential for tracing the circuits and identifying potential problem areas. These can often be found online.
If you're not comfortable working with automotive electrical systems, it's best to take your Corvette to a qualified mechanic specializing in classic cars or Corvettes. They will have the tools and expertise to diagnose and repair the problem efficiently. Attempting complex electrical repairs without proper knowledge can lead to further damage.
