should I use a relay for fuel pump?

I am finishing the wiring in our 39. the wiring harness I have has a single wire for fuel pump .I want to run a switch to cut off pump if I want. I will probably do the same for the ele. fan. Should I just run it thru a toggle switch or a toggle switch to a relay to the pump. is there any benifit to using a relay? any wiring diagahms for wiring relays would be helpful to see if what I have now is correct.

 

It depends on how long the wire run is, how thick the wire is, how much current the pump draws, and what other types of controls you want on the pump circuit.

Low current pump, short heavy wire, no funky control requirements means you can go without a relay. The opposite means a relay would be nice.

 

I run a Holley black pump right off my battery, through a fused 15 amp switch, 10 gauge wire, and grounded to the frame. Been this way for 5 years now. Neither the wiring nor the switch get warm to the touch. I did the same with my MSD box, so I effectively have 2 kill switches, and can operate either system independently of on another.

 

Not sure what you're trying to do, but if it's for anti-theft the use of a relay would allow you to use a hidden micro-switch. Just something to think about.

~ Carl

 

I like putting relays on things like fuel pumps, electric fans, and high and low beam headlights. I have run electric pumps in the past without one, but I find the pump gets more consistent current through a relay. It also takes some of the load off of the switch.

Don

 

For fire protection, the fuel pump should be wired through an oil pressure switch to kill the pump if the engine stalls. In this case a relay is good so the pump current doesn't go through the safety switch contacts.

 

I want a switch on the pump so I can turn it off while doing other ele. work or testing . Thanks .

 

thats a good idea.

 

I always run relays, simple reason is I switch both ignition and fuel seperatly. I also run a master battery kill.

 

does using a relay make it safer? was hoping some one would have a diagrahm showing how to wire relay with a toggle switch.

 

The relay takes the current out of the ign switch. Ford also uses a neat bump switch that opens with a fairly small impact.

 

I'm running a Holley Red [PN 12-801-1] on the p/u. Holley recommends wiring with a relay. I also am using a Ron Francis Crash Sensor Relay [CR-92] that comes with a relay included in the wiring. I like the Crash Sensor better than the oil pressure safety switch method for ease of install and function.

 

The "red fuel pump power wire" is what you connect to the switch, whether it's the ignition switch directly, the oil pressure switch, or the toggle switch.

 

I always run a relay for a fuel pump. Also, add an Inertia switch like mentioned before. Easy to find a good used one in any junkyard. Trucks are in kick panels, Mustangs and such are in the trunk.
Resets with the push of a button.

 

The oil pressure switch is a good idea, but if the limits are too high then you can't use your electric pump to prime the carbs before the engine starts.

Relays are used to take the big load off the switch and place the big load between the relay and the item being fed. Think of your starter solenoid as a big relay--- without it you'd need a huge switch and big cables running to your dashboard. I'm not a big fan of using relays unless it's really important because adding a relay is often adding another point of potential failure in the system. High load items probably should have relays, like headlights, but most manufacturers didn't bother with them back in the day and they certainly had plenty of relays to use if they wanted to.

If you have space for adequate wires and switches, then there's no need for a relay--- and fuel pumps are generally not heavy loads.

Another thought--- fuses, now that's something important and often overlooked. Make sure every load has a fuse and the fuse is the right size.

 

I love the enertia kill switch idea!! Just finished wiring up an electric pump in a '56 for a customer, I'm going to suggest that to him.

 

Will an inertia switch activate in a rollover? Like if you get sideways and roll off the road without a impact? A carbed engine will stall from a rollover leaving the vehicle on it's roof.The electric pump can continue to run,fuel pouring out of the carb vents while you're knocked stupid or fumbling around trying to get out.
This is the complication of electric fuel pump wiring...safety....Oil pressure or inertia switch,maybe a connection to the starter solenoid ballast resistor bypass to run the pump when starting,or a dash push button to prime the carb before starting...

 

A handy diagram for explaining things, thanks.

I always wire the "hidden" kill switch into the Black wire in that diagram. One black wire & a small switch. Ground at the switch where ever it winds up. That way the wire can be 20 gauge and easily routed / hidden.

B.

 

The oil pressure switch comes with a normally-closed contact as well as the normally-open contact. The normally-closed can be connected to starter solenoid. In the case you don't have fuel in your bowl, you crank a little more and the pump will fill the bowl.

 

Good advice, I wire mine the same Don

 

Primer button works well. I used one on my T roadster, but not in the dash. It's hidden.

Bob

 

hey thanks every one.I will use a relay on the pump and fan.I found some more wire diagrahms wich one of these is correct or is the87 and 30 terminal in or out?

 

Here you go, read this:

http://www.how-to-build-hotrods.com/electric-fuel-pump.html

It has all the info on how to do your electric fuel pump the right way, what kills electric fuel pumps, and diagrams on wiring it up...

 

i like the oil pressure switch cutoff idea with a primer button. never would have thought of this. thanks to everyone...jack

 

I hate inertia switches. I hate complicated things as well.

Relays are a great idea. The relay simply is an electric switch. So you have the power wire going to the relay then out to the pump. You have a thinner wire that activates the relay. The purpose of this, is to reduce switch failure, on longer runs of wire. My biggest reason is, its a pain the a$$ having thicker wire connected to a switch, Thinner is neater, and out of the way, this also adds to safety. So its a win win.

 

Thanks cherokee that was helpful

 

30 is power in
85 is ground
86 is switched power in
The 87 pins are power out

I also believe 85 and 86 can be swapped with no effects.

 

Remember to put your fuse as close to the battery as possible.

 

my rule of thumb is to put anything of somewhat heavy amp draw on a relay.. it takes the amperage off the switch, which is a good thing. and seeing relays are about 7 bucks it should be a no brainer...

 

The first 55 years of my hotrod life we never used a relay. The last ten there has been a big change on the internet anyway. To me a relay is just something else that can break and leave you on the side of the road. Of course I'm talking about the old Dupree/ SW style and other electric pumps for carbs. I always wire it through the key switch so I don't forget to flip the switch. I just turn the key to "on" and listen until clicking slows down, pump the gas twice and start it up. I believe in the KISS system. The less parts to break....the better. JMO