1. Safety First:
* Disconnect the negative battery terminal before working on any electrical components. This prevents accidental shorts and shocks.
2. Check the Fuel Pump Relay:
* Locate the fuel pump relay. Consult your owner's manual or a repair manual for the exact location. It's often in the under-hood fuse box or a separate relay center.
* Visually inspect the relay. Look for any signs of damage, burning, or corrosion.
* Swap the relay. This is the easiest test. Find a similar relay (same amperage and pin configuration) in the fuse box and swap it with the fuel pump relay. If the problem goes away, the relay is faulty and needs replacement.
* Test the relay (advanced): If you have a multimeter, you can test the relay's continuity and switching action according to its specifications. Repair manuals often provide these tests.
3. Check the Fuel Pump Inertia Switch:
* Locate the inertia switch. This safety device cuts power to the fuel pump in the event of a collision. It's usually located under the dash or in the engine compartment.
* Inspect the switch. Check for any signs of damage. Some have a small button that needs to be pressed to reset it. Push the button and see if the fuel pump starts working.
4. Check the Wiring and Connectors:
* Inspect the wiring harness. Look for any damaged, frayed, or corroded wires leading to and from the fuel pump, relay, and inertia switch. Pay close attention to connectors for corrosion or loose connections.
* Check the fuel pump connector. Make sure it's securely connected and the pins aren't corroded.
* Use a multimeter (advanced): With the ignition on, test for power and ground at the fuel pump connector. You should have power at one wire and ground at the other when the pump is supposed to be running. A lack of power or ground indicates a wiring problem. Trace the wires back to the relay and the computer (if applicable).
5. Check the Fuel Pump (Least Likely Culprit in Secondary Circuit Issue):
While the problem is *more likely* in the electrical system, a faulty fuel pump could cause a secondary circuit issue if it draws excessive current, causing a protection circuit to cut power. You can check the pump itself by:
* Testing for power at the pump connector (as above).
* Listening for the pump to prime. When you turn the ignition key to the "on" position (without starting the engine), you should hear a brief hum from the fuel pump. If you don't hear this, the problem is either electrical or the pump itself. However, if it's making a strange noise, it *might* be the pump itself.
6. Computer/PCM Involvement (Advanced):
On some 1990 Tempos, the fuel pump control might involve the Powertrain Control Module (PCM). A faulty PCM could cause a secondary circuit fault. Diagnosing this usually requires a specialized scan tool to read diagnostic trouble codes (DTCs) from the PCM.
Important Notes:
* Repair manuals are crucial: A Haynes or Chilton repair manual for your specific 1990 Ford Tempo will provide detailed diagrams, component locations, and testing procedures.
* Safety: Always disconnect the negative battery terminal before working on electrical components.
* Professional help: If you're not comfortable working with automotive electrical systems, it's best to take your car to a qualified mechanic. Misdiagnosis can lead to further damage or even injury.
This detailed troubleshooting guide should help you pinpoint the cause of your fuel pump secondary circuit fault. Remember to work systematically, checking each component and connection thoroughly. Good luck!
