1. Verify the New Parts:
* Fuse: Double-check that you're using the correct amperage fuse. A fuse that's too low will blow even with normal current draw.
* Relay: Ensure the relay is correctly seated and functioning. Try swapping it with a known good relay (from a different circuit, if possible, to rule out a bad relay).
2. Inspect the Wiring Harness:
This is the most likely culprit. A short can be caused by:
* Chafed wires: Look carefully at the wiring harness from the fuel pump relay to the fuel pump itself. Pay close attention to areas where the wiring might rub against metal parts, especially near the frame, suspension, or exhaust system. Look for any bare wires or areas where the insulation is damaged.
* Corrosion: Check the connectors at both ends of the harness (relay and pump). Corrosion can increase resistance and cause overheating, leading to blown fuses. Clean connectors with a wire brush and electrical contact cleaner.
* Broken wires: Carefully examine the wiring for any breaks or fractures, particularly in areas subject to movement or vibration.
3. Testing the Circuit:
* Disconnect the fuel pump: Disconnect the fuel pump wiring harness at the pump itself. If the fuse *still* blows with the pump disconnected, the short is in the wiring between the relay and the pump connector. If the fuse *doesn't* blow, the short is in the pump or its wiring at the pump.
* Use a multimeter: With the fuel pump disconnected, use a multimeter to check for continuity (a short circuit) in the wiring. Set the multimeter to the ohms setting. If you read a very low resistance (close to zero), you have a short. Trace the wire to pinpoint the location.
* Voltage drop test: This test helps isolate the exact location of the problem. You'll need a multimeter. Measure the voltage drop across different sections of the wiring harness between the relay and pump. A significant voltage drop (more than 0.5V) across a particular section indicates high resistance and is an area where the short might be.
4. Fuel Pump Issues (Less Likely, but possible):
* Faulty fuel pump: Even though it's less likely, a short *inside* the fuel pump can blow fuses. This is why disconnecting it is crucial for the troubleshooting steps.
5. Grounding Issues:
A poor ground connection can cause excessive current to flow, blowing the fuse. Check the ground connection at both the fuel pump and the relay. Clean them thoroughly.
Important Safety Note: Disconnect the negative battery terminal before doing any electrical work. Gasoline is highly flammable; take precautions when working around the fuel system.
If you're not comfortable working with automotive electrical systems, it's best to take your Cadillac to a qualified mechanic. They have the tools and expertise to diagnose the problem quickly and safely.
