When the circuit is open,...
When the circuit is open, the leads have no connection. No power is sent through the relay.
When the circuit is complete,...
When the circuit is complete, the connection is made between the feed power and the output. Power is now sent to the pump.
Step 2
Turn the key to the "off" position and disconnect the negative terminal on the battery. Examine the schematic on the relay itself; it should have a bunch of numbers and a bunch of symbols. To understand this, you have to understand how a relay works. A relay is like a door to two entrances. One entrance is always open, while one is always closed. A magnet inside the relay opens the second door when the circuit is complete and closes the previous one. On a Bosch relay, the numbers should correspond as follows: 30 is the feed; 87a is normally open; 87 is normally closed; 86 is trigger ground and 85 is the 12V trigger. If you bought a premade relay bottom it should be color-coded. Since we're only working with voltage going in one direction, 87a will not be used. You can de-pin this if you're using a premade connector. We also opted to de-pin the feed (30) since we're using a 12-gauge wire as our feed.
Step 3
Cut the 12V wire (blue with red) and wire it (side closer to the harness) to the 12V trigger on your relay (85). Do the same with the ground wire (white with purple) to the GND trigger on your relay (86). For the wire from your harness that goes to the fuel pump, wire the normally closed on the relay (87) to the other side of your 12V wire (blue with red). For the remaining ground wire (white with purple), crimp a ring terminal and attach it to an appropriate ground location. We used the continuity function on the voltmeter to find out that the fuel pump cover was a ground. Crimp a female terminal to your feed wire and attach it to your relay.
Step 4
Run the feed wire to the front of the car. Solder your feed wire to your inline fuse holder. Make sure to properly shield your connection with shrink-wrap or electrical tape. Crimp a ring terminal on the opposite side of the inline fuse holder and attach it to the positive terminal on the battery. Secure your wiring so that it is out of the way of damage. Make sure to insert a new 15-amp fuse into your fuse holder.
This is roughly what you should...
This is roughly what you should have when you're finished. Be sure to check all connections and properly secure the relay to the body.
Step 5
Check all of your connections, since a short in your wiring can cause an electrical fire. Attach the negative terminal to the battery. Turn the key to "on" to check if the fuel pump is working. It should momentarily turn on as it normally does if you wired it right. Start the car to check if everything is working properly. Mount the relay in a location that it cannot get damaged. Put everything back together and you're done.