Here's a breakdown of potential causes and how to troubleshoot:
1. Ignition Switch: This is the most likely culprit. The ignition switch is responsible for powering various circuits, including the fuel pump and fan, only when the key is in the "run" or "start" position. A faulty switch could be sending power constantly.
2. Relay Problems: Both the fuel pump and cooling fan are controlled by relays. These are electrical switches that activate the larger circuits. A stuck-closed relay for either the fuel pump or the cooling fan would keep them powered.
3. Wiring Issues: A short circuit in the wiring harness could be sending power to the fuel pump and fan even when the ignition is off. This could be due to damaged insulation, corrosion, or a loose wire touching a power source.
4. PCM (Powertrain Control Module) malfunction: While less likely to cause *both* the fuel pump and fan to run constantly, a faulty PCM could be sending incorrect signals to these components.
5. Aftermarket additions: If you have recently added any aftermarket accessories or modifications, they might have inadvertently created a short circuit or interference.
Troubleshooting Steps (Proceed with caution, disconnect the battery's negative terminal first):
1. Disconnect the negative battery terminal: This is crucial for safety before you start any electrical work.
2. Check the fuses: Inspect the fuses related to the fuel pump and cooling fan. Look for blown fuses (a broken filament) or fuses that are warm to the touch (indicating excessive current draw). Replace any blown fuses, but be cautious – if a fuse blows again immediately, you have a more serious short circuit.
3. Inspect relays: Locate the fuel pump relay and cooling fan relay. You'll likely need to consult a wiring diagram (often found online) to find their locations. Carefully remove them and inspect them visually for any damage. You can try swapping them with other relays of the same amperage rating (if you have spares) to see if the problem follows the relay.
4. Test for power: With the ignition OFF, use a multimeter to check for power at the fuel pump relay and cooling fan relay terminals. There should be NO power at any terminal. If you find power, you need to trace the wiring back to find the short. This requires patience and a basic understanding of electrical systems or professional help.
Important Considerations:
* Safety: Work on electrical systems can be dangerous. If you're not comfortable working with automotive electrical systems, take your car to a qualified mechanic immediately.
* Wiring Diagrams: Obtain a wiring diagram specific to your 1997 Mercury Tracer. This will be invaluable in tracing the circuits.
* Professional Help: If you cannot identify the problem after checking fuses and relays, it's best to take your car to a mechanic. The issue could be complex and require specialized tools and expertise. Ignoring the problem is highly risky.
Leaving this issue unresolved could result in serious damage to your vehicle or even a fire. Prioritize getting it fixed as soon as possible.
