Elec. Fuel Pump Wiring

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strange246

strange246

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Can any give me a simple wiring diagram to wire an elec fuel pump using a relay? Do I really need a relay? And can I use just a generic 30-40 amp relay? No oil pressure switch for now, just need to get it hooked up so I can start the motor for the first time

Ryan
 
In the schematic below substitute ignition crank/run power (from ignition switch...) to terminal #86 where it states black/blue wire from harness. I pulled this diagram off of the web for another specific application, but the wiring is the same. Make sure you use a quality 40 AMP relay. I cooked a Radio Shack 30 AMP relay after about 6 hours of run time. I still have to install the 40 AMP'er I bought and loose the toggle switch I "temporarily" wired in. 3 weeks ago.....

FuelPumpWiring-vi.gif


Ground the BLACK wire from the pump to a GOOD metal source. The RED goes to terminal # 30. When you power up terminal # 86, it gets it's ground from terminal #85. This closes the circuit and allows direct voltage to go from terminal #87 (direct from the battery) to terminal #30, straight to the fuel pump. This prevents a high-amperage situation from opening and closing directly through your ignition switch, which will eventually burn up. And don't use a toggle switch.... if you wreck and have a fire, the pump is pumping, and your dazed....*POOF*

As a side note, I believe the oil pressure switch cut-off splices into the ground side of the relay. Plan ahead and allow for this future modification as far as accessing and splicing into the exsisting circut your about to add.

Good luck!
 
While I was responding I see Joe stepped up with info too. I used 12 Gauge for ALL the fuel pump wiring. Remember, wire is like a garden hose: the bigger the gauge (diameter), the more it will flow. If the wire is too thin (18-20 Gauge) it's nothing more than a fuse.... waiting to light up. Otherwise good advice was added by suggesting buying a relay kit from Jegs or Summit, provided they supply decent wire and connectors. And speaking of connectors, solder the damn things on. Crimp-on connectors you use on the side of the road to get home, NOT to build a car with. Shrink wrapping those solder joints is a good idea too.

A mantra I used when building my car was "There's no kill like OVERKILL". I deliberately over-engineered certain things to prevent future headaches in areas that I wouldn't want to re-build, such as wiring and fuel line plumbing.
 
My electric fuel pump is wired without a relay. I have a toggle switch that powers it with the ignition in the "on" position.

Maybe a dumb question, but what is the purpose of the relay?
 
John is correct, most oil pressure switch setups go on the ground side.

The relay is to keep the ignition switch from having to handle all the current that the fuel pump draws. Just like the starter relay keeps the ignition switch from having to power the starter solenoid.
 
FASTBACK340 said:
While I was responding I see Joe stepped up with info too. I used 12 Gauge for ALL the fuel pump wiring. Remember, wire is like a garden hose: the bigger the gauge (diameter), the more it will flow. If the wire is too thin (18-20 Gauge) it's nothing more than a fuse.... waiting to light up. Otherwise good advice was added by suggesting buying a relay kit from Jegs or Summit, provided they supply decent wire and connectors. And speaking of connectors, solder the damn things on. Crimp-on connectors you use on the side of the road to get home, NOT to build a car with. Shrink wrapping those solder joints is a good idea too.

A mantra I used when building my car was "There's no kill like OVERKILL". I deliberately over-engineered certain things to prevent future headaches in areas that I wouldn't want to re-build, such as wiring and fuel line plumbing.
Click to expand...

Exactly!!! Solder and shrink wrap. You'll never regret it.
 
6pk2goDemon said:
My electric fuel pump is wired without a relay. I have a toggle switch that powers it with the ignition in the "on" position.

Maybe a dumb question, but what is the purpose of the relay?
Click to expand...

Even though a a good high quality switch is rated for 20A, it will alway last longer and the circuit itself will have much less resistance is a relay is used. 8)
 
I have to correct myself:

Above I stated never use a toggle switch because the fuel pump will still run if you wreck. Toggle switch or relay, it will still pump as long as the ignition is on.The OIL pressure switch cut-out is what I was thinking about. Too little sleep the past few days....
 
ramcharger said:
Even though a a good high quality switch is rated for 20A, it will alway last longer and the circuit itself will have much less resistance is a relay is used. 8)
Click to expand...

I HATE electrical and I wish I never decided to use an electric fuel pump :angry7:
Thanks for the lesson again :scratch:...... :homework:
 
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