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Old 09-19-2008, 10:48 AM
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Wiring diagram for electric fuel pump...

I need a wiring diagram for an electric fuel pump,
with a relay and oil pressure switch.

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Old 09-19-2008, 11:32 AM
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I don't have a diagram, but I can describe it.

Find a switched power source. Fused 10 ga wire goes into post 30 on the relay with a jumper to post 86.

Out from post 87 goes a 10 ga (or sufficient) wire to the fuel pump.

Post 85 will go to a normally-open oil pressure switch. That is to say, an oil pressure switch that grounds when it has pressure. There are switches that ground when there is no pressure, then open when there is pressure. If you have that kind of switch you're OK, just get a DPDT relay (it will have five prongs) and hook up the wire to your pump to 87a instead of 87.
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Old 09-19-2008, 11:46 AM
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Cool, thanks Curtis.
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Old 09-19-2008, 11:48 AM
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Quote:
Originally Posted by curtis73
I don't have a diagram, but I can describe it.

Find a switched power source. Fused 10 ga wire goes into post 30 on the relay with a jumper to post 86.

Out from post 87 goes a 10 ga (or sufficient) wire to the fuel pump.

Post 85 will go to a normally-open oil pressure switch. That is to say, an oil pressure switch that grounds when it has pressure. There are switches that ground when there is no pressure, then open when there is pressure. If you have that kind of switch you're OK, just get a DPDT relay (it will have five prongs) and hook up the wire to your pump to 87a instead of 87.

What if it's a cheap relay that only has "A, B, C, D, and E"? LOL
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Old 09-19-2008, 01:30 PM
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Quote:
Originally Posted by Jmark
What if it's a cheap relay that only has "A, B, C, D, and E"? LOL
Then I use the "plug and pray" method.
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Old 09-19-2008, 02:21 PM
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The information given is incomplete it does not allow the car to start with 0/zero fuel pressure ............................see this link

http://www.mr-gasket.com/pdf/110_140.pdf

page #3 figure 3 shows a digram and parts needed along with wiring

Last edited by pepi; 09-19-2008 at 02:29 PM.
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Old 09-19-2008, 02:46 PM
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Quote:
Originally Posted by pepi
The information given is incomplete it does not allow the car to start with 0/zero fuel pressure ............................see this link
While I agree, it doesn't make much of a difference. I used the wiring I described on my boat. First of all, the fuel in the bowls (if its carbed) will get you started and run for a while - long after the pump has already kicked on. Secondly, after a couple cranks of the engine there is enough oil pressure to kick the switch on, so even in something like a TBI it results in only another half second crank time. Third, on my boat after its been sitting for all winter, I just pull the wire off the oil pressure switch and ground it to the manifold for a couple seconds to fill the bowls.
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Old 09-20-2008, 01:23 AM
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On the relay,
30 goes to battery direct with fuseible link.
86 goes to the oil pressure switch.
87 to fuel pump.
85 to ground.

On pressure switch,
P is from relay 86.
S is to start circuit.
I is to switched ignition.
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Old 09-20-2008, 02:18 AM
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Quote:
Originally Posted by malc
On the relay,
30 goes to battery direct with fuseible link.
86 goes to the oil pressure switch.
87 to fuel pump.
85 to ground.

On pressure switch,
P is from relay 86.
S is to start circuit.
I is to switched ignition.
While that might work with some European cars, most oil pressure switches here in the US have one connection. Its a single connector that (depending on oil pressure) is either grounded or not. So I think for the problem at hand your wiring won't work.

I also have a problem with wiring the power supply from the battery. First of all, there is no reason to do it, and secondly, if the oil pressure switch fails in the closed position, the fuel pump will run continuously even with the switch off. That is why I wire the supply line from a switched source. Even if the oil pressure switch fails, you can continue to run the vehicle almost indefinitely until you get a new switch. You just have to be careful about how long you leave the switch on if the car isn't running.
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Old 09-20-2008, 03:33 AM
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That is not for European cars, only U.S. vehicles and I got it from a reputible
person dedicated to wiring American vehicles.
The recommended oil pressure switch is ACDelco G1809 costs $7.56 from
RockAuto.com and has three connections.
(GM 3986857 also)

I also have a problem with wiring the power supply from the battery. First of all, there is no reason to do it,

The pump needs a full 12 volts, that´s why.
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Old 09-20-2008, 03:37 AM
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For those hard to start cars you could build a primer circuit that runs the pump for 2 seconds when the ignition is turned on. Your ECM should do that anyway. For carbs just hook up a second circuit with a momentary switch so you can prime the carb if you need to. My carb setup will idle for 15 seconds or so without fuel pressure.

Where are you putting the oil pressure switch?
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Old 09-20-2008, 09:06 AM
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Here's a good post about electric pump & choke wiring. You can use the "R" terminal on the starter for power to the fuel pump before oil pressure builds up.
A question for you electric choke guys
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Old 09-20-2008, 10:24 AM
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LOL,,,don't guess!!!! test!!!!

many ign switches do also apply power to the "on" contact while in "start" position.....(so the pump will run in start)

on a switched source, if the volts at the coil doesn't drop at idle with the added pump amps your basically fine....
(compare coil volts with the pump hot wired to another cars batt to tell if the volts are the same at the coil at idle)

alot depends on the actual when running total amps load at idle versus alt at idle amps output if any....

a majority of the oem harnesses do have "some" reserve amps capability but,,, with age and use you do loose some of that reserve!

so my $.02:
switched or batt direct install depends on the specific application and which pump...
there are definitely good and bad points for either power source...
I would use a accident impact kill switch on a batt direct install!

Last edited by red65mustang; 09-20-2008 at 10:47 AM.
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Old 09-20-2008, 11:10 PM
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Somewhere in the vast wasteland of my mind I seem to remember something about using an oil pressure switch from a Vega to wire up a fuel pump.
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Old 09-21-2008, 01:17 AM
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Quote:
Originally Posted by jimfulco
Somewhere in the vast wasteland of my mind I seem to remember something about using an oil pressure switch from a Vega to wire up a fuel pump.
The oil pressure switch part numbers I gave are for a 74 Chevy Vega.
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