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Discussion Starter #1
Hey guys,

I'm hoping I can get some help here. I'm upgrading my in tank pump to an Aeromotive 340 stealth unit. Apparently it is a good idea to upgrade the pumps stock 14 gage wire when doing a big pump like this as the amperage is higher than the old 14 gage wire can handle sometimes. This is definitely a place where I do not want a fire.

Problem is, I'm not sure which wires to upgrade and how to do it. I'm hoping someone in here has done this mod before and can give me a step by step on how to do it.

There's not much out there on the old fox fuel wire upgrades but tons of thread on doing the later years.
 

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Most people that do this just find the pump relay and run larger wire from that relay to the pump itself. you can also upsize the wire before the relay if you want.
 

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Discussion Starter #4
I thought there was something about using a new relay, run new wires from new relay to fuel pump, new wire from battery to new relay, connect new wire to old fuel pump wiring to trigger new relay to come on.

Something along those lines.....


I sure hate to remove the seat as it's an aftermarket seat and a bear to get out/in with rollcage and everything. However, if that the way it is supposed to be done then that leaves little choice.
 

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The pump draws 15A, which is only good for 7' of un-deteriorated 14ga wire. Use 10ga wire for the new pump. The 10ga wire needs to be on both "sides" of the relay. That's the fused battery side coming in, and the power wire going out to the pump. Make sure you've got a good ground for the pump as well.
 

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Discussion Starter #6
Ross,

So do it as I explained above with a separate relay correct? NOT running new wire from the stock relay under the seat all the way back right.


I would use the normal power wire for the stock pump as the wire that turns on the relay. Is that right
 

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You can either wire in a new relay with new wiring and trigger it on with the old relay, or delete the old relay and power wiring (since it will now be dead weight) by using the oem trigger wires on a new relay with new power wires. There are a few diff ways that you can do it, each of which will perform the same in terms of current carrying capacity for the pump circuit.
 

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I would use the normal power wire for the stock pump as the wire that turns on the relay. Is that right
That'll work. You can run a 10ga wire straight from the battery or starter solenoid to your new relay to power the pump. Just make sure you fuse it (at the battery or solenoid).
 

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Discussion Starter #9
That's what I did.

Got 2 more questions just in case anyone knows the answer for sure.

On the stock power wire and ground that feeds the pump; I am now using the stock power wire to turn on the relay. Do I also need to ground the original fuel pump grounding wire? I'm kind of assuming that wire is already grounded somewhere since it originally served as a ground for the stock fuel pump. I'm assuming I can just cut it as it is no longer needed with the new setup.


Also the original fuel pump power wire can be ran with 14 gauge wire as it will not see much amperage to just turn on the new relay, correct?
 

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A normal battery on full charge is 13.8 volts, and while charging can be over 14.5.

The reason stock #16 wires works for some people is at 15 amps the voltage drop in 10 feet is about 0.6 volts. With a fully charged 12V battery on a running alternator you'll be at least 13.2 volts.

If you change to #10 (same 10ft length) you'll be at 0.15 volts drop, so you pick up 0.45 volts.

A good fuel system has way more headroom than that.

The ground wire length to the chassis also adds to the drop, as does the fuse and the relay contacts and especially any push-on connections. But as a general rule as long as you are not on the ragged edge of pump pressure or volume, you are OK at 15A in a car with an alternator with 16 ga with voltage.

My bigger worry with 16ga would be wire heat with minor overloads. A fuse does not blow exactly at the fuse current, it can sometimes carry 2 times or more the fuse rating for a minute or more depending on temperature and the fuse type, and any holder resistance at the fuse contacts. The OEM relay is also marginal.

I am helping a neighbor clean up the mess in his car and his fuel pump has an unnecessary 5-6ft long ground lead. It could have been a foot long.


Because of the heat and safety, and because the OEM relay is out of headroom on the contacts and probably old, I'd do like someone suggested and just pull a 10 or 12 wire and use a new 30-40A relay either driven from the old system some way. But I just wanted to point out why some people have no problems. It isn't really the voltage drop that is normally the real issue, it is the head room and safety.
 

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Discussion Starter #11
Thanks for the reply but I think you misunderstood my question.

I am using a new relay with 10 gauge power and ground wires to power the pump. The new relay gets power straight from the battery with a 10 gauge wire and a 10 gauge wire from relay to ground. The only thing I'm using the factory wire and relay for is to tell the NEW relay to "turn on". The factory wire will now therefore only see a maximum of 5 amps since it will only be telling the new relay to turn on.

FWIW though factory fuel pump wiring is 14 gauge wire.

Thanks again for the reply though. It will hopefully help someone out in the future who runs across this thread.
 

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What I did was......used the factory power wire to the pump to trigger a new relay that was feeding new heavier wire to the pump. Works fine no issues.
 
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