1. Identify the Problem:
* Does the indicator light not illuminate at all? This suggests a problem with the bulb, wiring, or the circuit itself.
* Does the indicator light illuminate incorrectly? It might show the wrong gear, flicker, or stay on constantly. This points to a problem with the sensor, wiring, or the instrument cluster.
* Does the indicator only work sometimes? This suggests intermittent problems with connections or wiring.
2. Troubleshooting Steps:
* Check the Bulb: This is the easiest first step. Access the instrument cluster (usually requires removing the bezel around the gauges) and check the bulb's condition. Replace if necessary. The bulb type will vary; check your owner's manual or a parts store.
* Check the Wiring: Carefully inspect all wiring related to the shift indicator. Look for broken wires, loose connections, or corrosion. Pay attention to the connection at the transmission range sensor (TRS) and the wiring leading to the instrument cluster.
* Test the Transmission Range Sensor (TRS): The TRS is located on the transmission and sends a signal to the instrument cluster indicating the selected gear. This requires a multimeter. You need a wiring diagram to identify the TRS connector and test for voltage and continuity. Testing the sensor itself often requires removing it from the transmission and testing its resistance with a multimeter (consult a wiring diagram for the proper test procedure and resistance values). A bad TRS is a common culprit.
* Inspect the Instrument Cluster: If the bulb and wiring are okay, the problem might lie within the instrument cluster itself. This is more complex and might require specialized tools or professional repair. A faulty printed circuit board inside the cluster is possible.
* Check the Neutral Safety Switch (NSS): While not directly related to the indicator light, a malfunctioning NSS can prevent starting and might indirectly affect the indicator light's behavior.
3. Repair/Replacement:
* Replace the bulb: A simple and inexpensive fix.
* Repair/replace wiring: May involve soldering broken wires, crimping connectors, or replacing sections of wire.
* Replace the TRS: This is a more involved repair and often requires mechanical skills to access and replace the sensor on the transmission.
* Repair/replace the instrument cluster: This is the most complex and potentially expensive option. It may be more economical to replace the entire cluster than attempt repair.
Important Notes:
* Wiring Diagrams: You'll greatly benefit from a wiring diagram specific to your 1985 El Camino. These are available online from various sources (e.g., Haynes repair manuals, online forums).
* Safety: Disconnect the negative battery cable before working on any electrical components.
* Professional Help: If you're not comfortable working on automotive electrical systems, it's best to seek professional help from a mechanic.
The repair process can be complex depending on the root cause. Start with the simple checks (bulb and wiring) and progressively move to more involved diagnostics. Remember to consult a wiring diagram for your specific vehicle to avoid damaging other components.
