Here's a general guide, but consult your vehicle's wiring diagram for precise wire colors and locations. The diagram should be in your owner's manual or available online through repair manuals like Chilton's or Haynes.
Understanding the System:
The fuel pump in your 1987 S10 Blazer likely receives power through a relay, which is controlled by the engine control module (ECM). This ensures the pump only runs when the ignition is on and the engine needs fuel. The relay switches a higher current circuit to power the pump, protecting the ECM's delicate circuits.
Typical Wiring (using a relay):
1. Power Source (Battery): A heavy-gauge wire (usually red or red/black) runs from the battery's positive (+) terminal to the relay. This wire carries the high current needed by the fuel pump. This is often a fused circuit.
2. Ground: A ground wire (usually black) connects the fuel pump to a good chassis ground. This completes the electrical circuit.
3. Relay Coil (Control): Two smaller wires connect to the relay coil. These wires control whether the relay is activated:
* Ignition-Switched Power: This wire (often a light-gauge wire, various colors) provides power to the relay when the ignition is turned on. This is often connected to the ignition switch directly or through a fuse.
* Ground (Relay Coil): This wire (often a light-gauge wire, often dark) completes the circuit to the relay coil. This ground is often provided by the ECM or a related sensor (like the crankshaft position sensor). The ECM signals to ground this wire, activating the relay.
4. Relay Output (to Fuel Pump): Two more heavy-gauge wires are connected to the relay:
* Power to Fuel Pump: This wire (heavy gauge, red or similar) carries power *from* the relay *to* the fuel pump.
* Return from Fuel Pump: This wire is the return path from the pump to the relay. (Though not strictly "returning" power; it's a complete circuit).
Steps for Wiring (with relay):
1. Identify wires: Use your wiring diagram to locate the correct wires. Carefully trace them to the fuel pump and relay.
2. Connect to the Battery: Connect the heavy-gauge wire from the battery positive (+) terminal to the relay's input terminal. Make sure this is fused appropriately.
3. Ground the Fuel Pump: Connect the fuel pump's ground wire to a clean, unpainted metal surface on the chassis.
4. Relay Connections: Connect the ignition-switched power and ground wires to the relay's coil terminals.
5. Fuel Pump Power: Connect the heavy-gauge wires from the relay output terminals to the fuel pump.
6. Test: Carefully reconnect the negative battery cable. Turn the ignition key to the "ON" position (without starting the engine). You should hear the fuel pump prime for a few seconds.
Without a Relay (Less Common):
Some older or simpler systems may run the fuel pump directly from the ignition switch. This is less common and generally less desirable, as it puts a higher load directly on the ignition switch. If this is your situation, the wiring is simpler, but it increases the chances of overloading the ignition switch.
Important Considerations:
* Safety: Work in a well-ventilated area. Fuel is flammable.
* Fuse: Always use an appropriately sized fuse in the power line from the battery to protect the circuit.
* Professional Help: If you're uncomfortable working with automotive wiring, it's best to seek professional help from a mechanic. Improper wiring can lead to fire or vehicle damage.
This information is general. You MUST use your vehicle's wiring diagram to ensure correct wire colors and locations. Failure to do so could result in a malfunctioning or unsafe system.
