Heavy Duty Fuel Pump Relay Wiring Instructions
Scott Simpson - Scott231@Juno.com
To supply additional voltage to the fuel pump to ensure full pressure and volume at Wide Open Throttle. The factory setup only supplies voltage to the fuel pump from the fuse panel; which varies from 11.0-12.0 volts. By feeding the fuel pump voltage from the alternator, the voltage is raised to 13+ volts.
Parts Needed
A 20 or 30 amp relay (4 or 5 prong; Radio Shack part #275-226 works great,) 15 feet 10 or 12 gauge wire, 2 feet 16 or 18 gauge wire, in-line fuse holder with 25 or 30 amp fuse, spade connectors, test light, solder & soldering iron. All connectors should be crimped and then soldered to eliminate the possibility of a bad connection. Total parts cost should be less than $20!
Trigger circuit -

    Locate a spot for mounting the relay under the hood and connect prong 85 to a ground with about 1/2 the small wire. Use the other half of the wire to connect prong 86 to the Fuel Pump Primer wire behind the alternator (Black connector/Gray wire) using a male spade connector. You can now turn the ignition to ON and you'll hear the relay kick on.

Power circuit -

    With ignition OFF, use about 1 foot of the large gauge wire to connect prong 30 to the hot post of the alternator (remove black cap, loosen nut, use an eyelet connector). Splice in the in-line fuse holder to this wire for safety purposes. The remaining prong on the relay is the "Power Out" that will feed alternator voltage to the pump(s).* Run the remaining heavy gauge wire from the appropriate "Power Out" prong on the relay under the firewall and through the fame rail to the gas tank connector under the rear bumper.

    The 3 wires going to the sender/pump are Black-Ground, Pink-Fuel Level Sender, and Brown/White Stripe-Fuel Pump motor (on some cars this wire may be Gray.) Cut the Brown/White Stripe wire (after the 3-wire connector by bumper) and connect the large gauge wire from the relay to the section of the Brown/White Stripe wire going to the pump. If you have multiple pumps, you need to run the wire to both of them so that both pumps see the same voltage. Pump(s) will have a louder "whine" under all conditions. Re-check fuel pressure as the additional voltage may make a big difference to your setup.


    * If you have a 5 prong relay the two remaining prongs should be labeled 87 and 87a. One is the "Power Out" when relay is energized, the other supplies power when the relay is not energized. Use a test light to determine.

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