Electric Fuel Pump/relay???

[h2ojet001]

I am going to be installing a relay for the fuel pump and have a few questions. How close to the fuel pump should the relay be mounted? What gauge wire should I use for the wire going from the switch to the relay? Should the +12 going to the switch come directly from the battery or off the ignition when the ignition is turned on. I see that painless wire has a kit for connecting a relay to the fuel pump. Has anyone used it? If you have any pictures showing the mounting of the relay it would be helpful. Thanks
Barry

[myoung]

It really doesn't matter where you mount a relay, it works the same regardless. The wire that switches the relay can be quite small, 16 or 18 ga., it wont be conducting very much amperage, less then 1 amp. It doesn't matter where you get your 12v supply from, just as long as it will support the amperage draw of what you're turning on with the relay. One of the purposes of a relay is to eliminate the number of switches and connectors the supply has to go through to avoid current drop, so a source straight from the battery is the ideal way to go. Also, if you took it off the key switch, you wouldn't need the relay in the first place. The Painless kit is nice because it comes with everything you need and the relay socket is nicer than the taiwan ones you can buy at the autoparts store.

[sdba069]

I don't fully agree with that last deal. I recommend that you run the relay as close to the pump as possible. I would run a 12 gauge supply wire from the battery to the relay for the power source, maybe larger if it has to run a long way. One thing is cetain, you pretty much can't run too large a wire. As far as the switch for the fuel pump, in a lake boat, I run the power for the switch from the ignition switch ignition post so that the key has to be on for the switch to have power, then run the command wire to the relay. I route the ground wire for the relay through a low oil pressure switch so that if the engine were to die, the fuel pump would shut off. You can install a bypass switch, if you desire, in the ground circuit, so that you can run the pump without the engine running. For what it's worth, I run relays on almost everything in a boat or a race car that has current draw that amounts to much. Hope this helps.

[myoung]

Just curious why you recommend mounting the relay at the pump. Been doing this a very long time and never heard that before, just wondering what your reasoning is. I could see if the fuel pump drew a ton of amps needing this, but I've yet to see that situation. Not flaming, just curious.

[sdba069]

You mentioned in your earlier post that one reason was to minimize the number of switches that power was transferred through, but you actually add another switch when wiring in the relay. Now, back to your question. I probably over emphasized the close deal, and really anywhere between the battery and the device will do as long as the supply wire is of adequate size. Probably more of a personal thing. I'm thinking probably, the distance between the relay and the device you are powering should be kept to a minimum to decrease the amp draw through the relay. Probably not that big a deal, but it works for me and always has. I rig lots of boats and wire lots of race and Pro Street cars and there is absolutely never a problem with this method. Everyone has their own ideas and I guess whatever works for you.

[myoung]

That's cool, just curious.
You mentioned in your earlier post that one reason was to minimize the number of switches that power was transferred through, but you actually add another switch when wiring in the relay.
Well, yes and no. You don't add another switch in the power circuit, you add a switch to turn the relay on. That or you use an existing switch to turn on the relay you've added to a circuit instead of running a high amp circuit through that swich. Not the same thing as having an existing circuit and adding yet another switch to it.
In my post I was referring to the fact that a relay handles the powering up for a device instead of running the power all the way through a switch on a dash via plugs and connectors and wire back and forth and losing amperage along the way. With a relay there is only one switch between the source and the device when wired straight to the battery, that switch being the relay itself. Any bypass switches can interupt the control wire going to the relay and plugs and such can be reduced to a minimum on the power circuit.
I have about 25 years wiring vehicles and have settled on the ways that I do things as well, but I'm always keeping my eyes open for other ways to do stuff. It's like anything else where there is more than one way to do something and they all get the job done. :wink:

[sdba069]

That'll work................

[h2ojet001]

I understand the necessity of having the fuel pump as close to the relay as possible and having the power source also close to the relay. Since my battery and fuel pump are fairly close together I can make a small bracket and mount the relay near the fuel pump. This should take care of the low voltage at the pump. Thanks for the input
Barry

[sdba069]

You are welcome.