3 prong oil pressure switch elec. fuel pump wiring

[newtoboat101]

hello, changing from 1988 mercruiser 5.0 lx /alpha 1 gen 1 ,to new gm 5.7 vortec motor with electric fuel pump. wire from I terminal goes to ? and the S terminal wire goes to ? have a thunderbolt4 ignition with delco est distributor ,My confusion is the purple wire to neutral safety switch is where i should tap into ,i have no purple wire going to starter ,or should i bring S terminal from switch to starter post ,i believe its the yellow /brown wire on starter or i have terminal on starter that has no wire to it so right now i have carter pump 43?? , 30 amp relay and circuit breaker, 3 prong oil pressure switch, like the picture attached

 

[alldodge]

Your diagram is confusing.
This is a simple way to use which I modified from a vega drawing. It doesn't use a relay and @Rick Stephens has one with

 

[Rick Stephens]

Your harness will not have the purple/yellow wire in it, that came out in '92/'93 when electric fuel pumps replaced mechanical.

The starter motor on my '90 motor did not have the outer 'fuel prime' lug for the pur/yel wire either. I thought about using another relay and going off the yellow/red starter actuator lug. In the end a new starter was simpler solution to maintain over time.

This is achris's diagram.

 

[newtoboat101]

thank you very much

 

[newtoboat101]

hello, all, i have hooked up my electric fuel, but have question ,and that is :when i turn the ignition to the on position the pump runs continuously ,is that correct? i have a 3 prong oil pressure sensor with a 5 wire relay (30,85,86,87,87A), i was under the assumption the pump would come on for a second or 2 ,then turn key to start ,switching to oil pressure,now heres where my wiring differs from the above ,i do NOT have purple wire going to starter,so i put S prong from oil pressure to the purple wire on back of alternator,could this be my error why pump stays on ?

 

[newtoboat101]

another question .because i dont have a purple wire going to my starter,but my starter looks to have an outer post ,can i splice into the purple wire from coil to run down to starter outer post and then run purple wire up to S on 3 prong oil pressure switch ,or if starters outer post doesn't work still wire this wire and get new ,electric pump compatible starter

 

[Rick Stephens]

Sounds like you are wired incorrectly. Turning on the key should not power the fuel pump at all, ever. There are only two ways for the pump to get power:

1) The starter is cranking and the outside lug provides power to what on an OEM harness is the purple/yellow wire going to the pump.

2) The oil pressure comes up and the oil pressure switch powers purple/yel to pump

If your ignition turns on the pump you have succeeded in building a bomb.

 

[newtoboat101]

thanx rick stephens, i think i had it hookup correct ,but because the pump did nothing i switched my wires up try to get something out of pump, will be hooking back up . i am timid on starting my motor to see if pump works ,because its a brand new motor that i primed but has never been started yet,can an ohm meter help in determining if if pump is getting power when ignition is turned on ?Also on a side note for rick stephens in another post on electric fuel pumps you put a picture up showing your fuel pump and kicker motor hookup from fuel line coming from water /fuel separator ,how does that work for you ,i tried that hook up last year ,but main motor had mechanical pump ,and i could not get it to feed fuel ,i had on/off valve like you show .

 

[alldodge]

With a 3 wire oil switch you only use 2 of the terminals. Common and Normally Open contact.

Pin 85 and 86 are the relay coil to energize the relay
Pin 30 is common
Pin 85 is NO and pin 85A is NC

but my starter looks to have an outer post ,can i splice into the purple wire from coil to run down to starter outer post and then run purple wire up to S on 3 prong oil pressure switch

NO
This will cause all kinds of problems
That outer post can be used to power up the relay to energize the pump as in Ricks post

 

[Rick Stephens]

Note: Purple wires are HOT when the ignition is turned to run. The ONLY things that go on purple are ignition, gauges, choke, oil pressure switch for the fuel pump and alternator excite.

The outer lug on the starter is HOT when the starter is cranking. Its sole purpose is to run an electric fuel pump during cranking and is powered by the starter solenoid.

Purple yellow is normally the power wire to the fuel pump. There are two wiring methods to power the purple yellow at the fuel pump:

1) Direct from the oil pressure switch and direct from the outer lug of the starter. Those two source wires come together anywhere along their length, usually at the pressure switch, making a stock purple yellow power circuit.

2) Power can come from a relay. In this case the relay on the output side goes to the fuel pump. Input side is from battery plus. Switching is from BOTH oil pressure switch and starter outer lug.

In both cases you can run your fuel pump by itself by shorting the battery lead at the starter solenoid to the outer small lug. I do this every spring to prime my carburetor first time I start it. This usually means I can start the motor with two pumps on the throttle and a half revolution of cranking. You can also turn ignition on and short the two terminals on the oil pressure switch to prime.

The manifold/filter mounting head for a fuel water separator has two input source ports and two output ports. I have had no issue with having the kicker on one of the output. At first I had a primer bulb inside right next to the filter, I think Bondo pointed out that isn't legal since it is not fire resistant. Now I just use the regular primer bulb on the kicker hose close to the motor. It works fine, just needs more pumping since it has to pull fuel. I also have a shutoff in case I ever get an air leak on that line. The setup requires good seals at all connections.

 

[newtoboat101]

thanx alldodge and rick stephens, .alldodge i do not have a 85A on my relay ,i have 87 and 87A ,So i have to question that but everything else ,i think i finally understand .Rick stephens ,maybe i didnt have good seal on kicker motor to get fuel to motor rick stephens ,i believe my shift cutoff solenoid is also connected to purple wire to coil ,if im correct

 

[alldodge]

thanx alldodge and rick stephens, .alldodge i do not have a 85A on my relay ,i have 87 and 87A ,So i have to question that but everything else ,i think i finally understand .Rick stephens ,maybe i didnt have good seal on kicker motor to get fuel to motor rick stephens ,i believe my shift cutoff solenoid is also connected to purple wire to coil ,if im correct

My mistake, the second mention of 85 and 85A should be 87 and 87A

 

[Rick Stephens]

Purple does not go to the shift interrupt. It grounds the Thunderbolt ignition, not the hot wire. Would melt stuff if it grounded purple.

 

[newtoboat101]

thanx guys

 

[newtoboat101]

Hello all , have another question .As i stated before this is a fresh never started new motor,so if i have all my electric hooked up correct ,can i prime the motor ,while having ignition on ,will that fuel pump kick on when i get oil pressure up to test my electric pump system?

 

[newtoboat101]

what i mean by prime is ;take dissy out and prime oil pump to build oilpressure for 3 prong oil pressure switch

 

[alldodge]

Yes, with power to motor,, once oil pressure builds the pump should run

 

[newtoboat101]

awesome thanx

 

[newtoboat101]

hello all, i took the distributor and primed engine ,turned ignition to on and the fuel pump would come on everytime i got a little pressure in oil pressure switch .SUCCESS! thank you so so much