Fuel pump wiring question

Joined
Jan 6, 2012
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I have installed a higher output fuel pump for my land cruiser for the v8 swap. The stock wire size is what looks like 16 or 18 gauge and is about 8 feet long or so. The fuel pump pulls a maximum of 20 amps. The oem power wire has 3 plugs. One before the rear fender where it goes through the floor, one on top of the fuel tank, and one at the tank where it goes through the sender. I ran 12 gauge wire at the relay to about 3" before the first connector. The last 3 inches of wire before the plug is still 18 gauge. I was going to cut about 3" after the first connector in splice in more 12 gauge wire, and do the same at the second connector and at the tank. How will this affect overall resistance in the circuit? Is it a big enough deal where I should install new pins in the plugs and eliminate all 18 gauge wire?
 
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Looks like you're about the maximum amperage for 18 gage at 20 amps depending on the wire type. But I can't believe the pump would pull anywhere near that steady state. As far as resistance looks like 18 gage is 4 times the resistance of 12 gage per foot - but that's 6.5 ohms per 1000 ft versus 1.5 ohms per 1000 ft.

So for 6 inch runs of 18 ga you're not really adding any serious resistance as far as voltage drop goes. Run it and if something melts then you know lol.
 
Joined
Jan 6, 2012
Messages
7,701
Looks like you're about the maximum amperage for 18 gage at 20 amps depending on the wire type. But I can't believe the pump would pull anywhere near that steady state. As far as resistance looks like 18 gage is 4 times the resistance of 12 gage per foot - but that's 6.5 ohms per 1000 ft versus 1.5 ohms per 1000 ft.

So for 6 inch runs of 18 ga you're not really adding any serious resistance as far as voltage drop goes. Run it and if something melts then you know lol.
I test drove it with only the 18 guage wire and nothing got hot or warm except the relay I used was warm. Its a toyota relay rated for 22amps. The wiring itself did not get warm. I guess my main concern is wiring at the tank melting as that could cause a fire. But if the 18 gauge wiring didn't get warm along the rocker on my test drive and didn't seem to be a big issue, is it even less of an issue with only like 6 or 12" of 18 gauge? Im thinking it is less of an issue but I don't completely understand why, Im ok at wiring but Im not an electrical wizard.
 
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I'd say you won't have an issue at all, especially if you couldn't feel any warmth in the 18 gage. If you ever have the chance to have someone put a clamp on DC ammeter I'd be curious to see what the pump actually draws while running. I bet it's no more than 10 amps.
 
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