Im installing a new aerospace fuel pump and my friend says I should install a relay. I have been running a holley black pump with no relay for years with no problem. I need some input.

Definately relay. Painless makes nice ones that are all color coded and easy to install.

I have relays on everything

The point of a relay is because most switches are only rated for a couple of amps. If the pump draws more amperage than the switch is rated for then the switch blows and you're dinked. If you run a relay then the power through the switch is a) constant and b) low amperage. The relay will flow more amperage than a switch so when the pump wants the amps the relay will let it have it. However, you need a relay with a higher amperage than the pump and you need a fuse of a lower amperage than the relay so that neither the pump nor the relay are overloaded.

Let's say you have a pump that "can" draw 10 amps. It will draw this only when it meets resistance (like full float bowls and no return lines). Normally it would draw maybe 1 or 2 amps.

So ...
1) You run power through a 2 amp switch to energize the relay. 14 ga wire.
2) You run separate power in one side of a 15 amp relay. 12 ga or 10 ga wire
3) You run 12 or 10 ga wire out of the relay through a 10 amp fuse to the pump.
4) Ground the pump.

Note the relay is rated higher than the pump, the fuse lower than the relay and the wire is sufficient to handle the current.

When you flip the switch the relay is energized and allows the current to flow through the fuse to the pump. If the pump is overloaded it blows the fuse without harming the rest of the circuit.

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no relays fan,water or fuel pump,anywhere here. step up one wire size and use a 40 or 50 amp switch

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That's ridiculous ! It would be like running power thoughout your house right from the transformer - with no breaker panel !!! When something shorts it just burns your house down.

Same applies to the car. So instead of blowing a cheap fuse the pump overloads, melts the insulation off the wire, shorts to the chassis and blows up you battery or lights the whole thing up.!

What some guys do to save a few bucks !!!!

Fred didn't say he doesn't uses fuses, just no relays. He is correct relays save switches. If you do use a high quality enough of a switch you can get away without a relay.

I now use fuses and relays were ever possible, saves on the big gauge wire runs.

No relays! More than sufficient assuming all is fused.

Relays don't protect the circuit. Relays are not protective devices. Fuses, circuit breakers, fused links, and PTC's are protective devices.

If the conductor is large enough to handle the current and the switch is designed to handle the current, and the circuit is fused, then it's not a flawed circuit.

Afterall, the relay is simply a electromagnetic switch.

Relays are not required. Period.

But in this case, on my Car, I used a relay to shorten the run of heavy ga wire. Since the toggle and control of the pump is in the front of my car and the battery is in the back. I used a very short run of 10 ga wire from the battery to a fuse and then through the relay to the pump. Then I used an 18 ga wire from the cars original fuse panel to the toggle sw and to the relay in the back of the car.

To relay a component you should consider the amperage and location of the component. Relays for the fuel pump are often used due to the fact that they are very close to the battery in most race cars so if you relay it you won't need to use such heavy wire. I use a blue pump and it doesn't use many amps so I don't have to have a relay. IMO relays are only necessary to cut down on the wire size that you are required to use. Fuses and proper wire size are in place to keep you from melting wires not relays. I do run my fuel pump off of the same fuse/relay as my water pump so that if the water pump stops so does the engine. I don't like to use relays if it's not necessary because it's just one more thing to fail during the race day. The relays that I do use are not those funky little square plastic things. I have two 100% duty cycle heavy duty relays(they look like Ford stater relays)One runs my fan the other runs the water pump and has a wire that goes all the way back to my fuel pump. I've used the same relays for many yeas now without fail.

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Fred didn't say he doesn't uses fuses, just no relays.

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Yep, good point!

Thanks for all the input. I just orderd a painless fuel relay kit. In addition to the new pump I bought the aerospace filter and regulator. Also ran 10an line from back to front. Now all I need is the aluminum heads.

just to clarify it. i run fuses as well as relays.
everything is also run with weatherpack connectors for easy installation and removal.

funny that in all the hooting and hollering about how great relays are no one mentioned that you don't have to use switched positive to operate the relay. you can just power one side of the coil from the positive you're using for the feed and switch the other side to ground. that way you have less live circuits in the car.

relays are not mandatory and are no substitute for proper craftsmanship in wiring. imho they're most often used because people either don't have a good grasp of electricity and/or don't use quality materials which often are more expensive and difficult to source. i've done current draw tests on different ignitions, fuel pumps, trans brakes, electric shifters and fans. the fans are by far the largest load with some of them at 15 amps or above. certain types of electric shifters and trans brakes can pull a decent amount as well. i've rarely if ever seen a fuel pump or ignition pull more than 10 amps.

unnecessary parts left out cost no money, reduce complication/weight and cause no service problems.

Any circuit should be protected with fuses or circuit breakers or fuseable links. It dont matter if you use a relay you still need to protect the circuit with a fuse or equivalent. The best I can think of is to think about a starter relay. Now if you had a switch to handle 200 to 400 amps would you still want to run battery cable size wire up in the dash to the ign switch ??? No of course not ! Thats why you use a starter relay so it can handle the heavy load and keep the large starter cable wire under the hood. I used a relay for my electric fan I installed on my 63 but I could have done it without one. This way I just use 18 gauge wire to the switch that works the relay and then I used 14 gauge wire to the relay. Both circuits are protected which are the relay coil circuit from the switch which is on a 10 amp fuse and the load carrying wire that goes to the relay contacts which is protected by a 30 amp fuse. Its just a matter of the circuits being run and the load the circuit will carry. I have always said that the Japanese cars use way to many relays as they take a simple circuit that needs one relay and end up having 3 relays in it. Ron

Relays have their place,I choose to run good switches and heavy wire on all runs shorter than 10ft, The only relay we have is on the fuel pump cause its in the rear with the batts and hot fed from the batts with a relay switching the pump, some guys relay everything, it just makes for more wire and some thing else to go wrong, relays are not fond of vibrations or wet locations, that's why they use so many of them in marine gensets, makes for a lot of service calls