Wiring elec fuel pump questions, relay location? oil pressure and or inertia?

[Cudakiller70]

Looking for some help and guidance since electrical is not one of my strong points.

Relay location
Instructions recommend mounting the fuel pump relay close to fuel pump which is mounted by the gas tank. To do this I'm thinking a good spot for the relay would be in trunk, but since my battery is up front this means running 10 ga constant hot wire to the trunk, or if mounting the relay under dash  would be better to have a switched wire going to the pump. Which would be better? Does it really matter?  Over thinking this?

Oil pressure switch
This seems like a good thing to do, but from what I've seen it looks like the pump does not turn on until cranking starts? I want the pump to run when ign switch is turned on, before cranking to fill carb bowls. Is there a way to do this with a bypass switch? Or any other options? What do you suggest?

Inertia switch
Still need to get, where in the circuit would be best to wire in?

[Cuda Cody]

Over my head.  Sorry I can't be more help, I've never done one.

[1 Wild R/T]

Must be a big pump if it needs to be fed by a 10 ga wire...  That said, if your gonna use an oil pressure switch logic dictates trying to minimize how many wires travel front to back...   Unless of course you own a copper mine..     So your trigger for the relay will come from the front, whether your using a output from a controller or a switched ignition feed, run that forward to your oil pressure switch,  output from the oil pressure switch goes to the relay connector socket 86 next you need a ground for the relay control, any solid metal ground in the trunk is fine, connect that to one side of the inertia switch, other side of the inertia switch goes to socket 85 of the relay connector....  Next is your 10 ga which I would probably connect to the big lug on the starter...  That connects to socket 30 of the relay & finally the lead to the fuel pump goes to socket 87 of the relay...

On the wire from the oil pressure switch to socket 86, add a momentary contact push button to prime...

Oh, inertia switch, I'd grab a Ford switch, they are easy to mount, reliable & cheap.... bolt it solidly to a stout brace like the trunk hinge area...

[Cudakiller70]

Thanks Wild R/T
This is the schematic I have.

[GoodysGotaCuda]

I used an intertia switch on my car on the relay control side [ground]. Distance of the relay compared to the pump is somewhat irrelavant, the run length is the run length. As long as the proper fuse is as close to the power source [ideally the battery], and the wire between the power source and pump is sufficient for the distance, you are good [10ga is more than fine].

I would not use an oil pressure switch, it wont prime until it's cranking and just because a car is hit doesn't mean the engine will stop running [it likely won't]. Adding another momentary priming button and sensor is just adding more potential sources for failure, combined with the additional complexity, it is hard to justify.



My inertia switch is just to the right of my ECU, it is up front since that is near the relay/fuse box.

[1 Wild R/T]

I used an intertia switch on my car on the relay control side [ground]. Distance of the relay compared to the pump is somewhat irrelavant, the run length is the run length. As long as the proper fuse is as close to the power source [ideally the battery], and the wire between the power source and pump is sufficient for the distance, you are good [10ga is more than fine].

I would not use an oil pressure switch, it wont prime until it's cranking and just because a car is hit doesn't mean the engine will stop running [it likely won't]. Adding another momentary priming button and sensor is just adding more potential sources for failure, combined with the additional complexity, it is hard to justify.



My inertia switch is just to the right of my ECU, it is up front since that is near the relay/fuse box.

I've always seen the oil pressure switch as a safety to keep from having the pump running if the key is on & the engine dies or looses oil pressure... I had a customers carbureted engine stall due to a stuck float, he didn't switch the key off & it wound up filling the engine with fuel....  If it had an oil pressure circuit that wouldn't have happened...

[Chryco Psycho]

To minimize wiring you could put the relay at the front & just run a single power wire to the rear with a fusable link in the circuit to protect it have the low amperage trigger wire go through the oil pressure switch with a bypass switch to prime the engine . you can also use the  oil pressure switch on the ign feed using a relay so if there is no oil pressure the ign also shuts down again with a bypass so you can start the engine .

[GoodysGotaCuda]

I used an intertia switch on my car on the relay control side [ground]. Distance of the relay compared to the pump is somewhat irrelavant, the run length is the run length. As long as the proper fuse is as close to the power source [ideally the battery], and the wire between the power source and pump is sufficient for the distance, you are good [10ga is more than fine].

I would not use an oil pressure switch, it wont prime until it's cranking and just because a car is hit doesn't mean the engine will stop running [it likely won't]. Adding another momentary priming button and sensor is just adding more potential sources for failure, combined with the additional complexity, it is hard to justify.



My inertia switch is just to the right of my ECU, it is up front since that is near the relay/fuse box.

I've always seen the oil pressure switch as a safety to keep from having the pump running if the key is on & the engine dies or looses oil pressure... I had a customers carbureted engine stall due to a stuck float, he didn't switch the key off & it wound up filling the engine with fuel....  If it had an oil pressure circuit that wouldn't have happened...

There are reasons to and not to use it, for me, I prefer to omit it.

[1 Wild R/T]

I used an intertia switch on my car on the relay control side [ground]. Distance of the relay compared to the pump is somewhat irrelavant, the run length is the run length. As long as the proper fuse is as close to the power source [ideally the battery], and the wire between the power source and pump is sufficient for the distance, you are good [10ga is more than fine].

I would not use an oil pressure switch, it wont prime until it's cranking and just because a car is hit doesn't mean the engine will stop running [it likely won't]. Adding another momentary priming button and sensor is just adding more potential sources for failure, combined with the additional complexity, it is hard to justify.



My inertia switch is just to the right of my ECU, it is up front since that is near the relay/fuse box.

I've always seen the oil pressure switch as a safety to keep from having the pump running if the key is on & the engine dies or looses oil pressure... I had a customers carbureted engine stall due to a stuck float, he didn't switch the key off & it wound up filling the engine with fuel....  If it had an oil pressure circuit that wouldn't have happened...

There are reasons to and not to use it, for me, I prefer to omit it.

In your application your PCM should kill the fuel pump if theres no IDM signal along with being EFI you have a closed system, fuel will just return to the tank....  Think back to when you ran a carburetor... Not saying it's a must have but there's enough value that a lot of OE's felt it was worth having & we all know how the bean counters chop un-needed over engineered systems...  Then again the bean counters need to think about lawsuits...

[GoodysGotaCuda]

I used an intertia switch on my car on the relay control side [ground]. Distance of the relay compared to the pump is somewhat irrelavant, the run length is the run length. As long as the proper fuse is as close to the power source [ideally the battery], and the wire between the power source and pump is sufficient for the distance, you are good [10ga is more than fine].

I would not use an oil pressure switch, it wont prime until it's cranking and just because a car is hit doesn't mean the engine will stop running [it likely won't]. Adding another momentary priming button and sensor is just adding more potential sources for failure, combined with the additional complexity, it is hard to justify.



My inertia switch is just to the right of my ECU, it is up front since that is near the relay/fuse box.

I've always seen the oil pressure switch as a safety to keep from having the pump running if the key is on & the engine dies or looses oil pressure... I had a customers carbureted engine stall due to a stuck float, he didn't switch the key off & it wound up filling the engine with fuel....  If it had an oil pressure circuit that wouldn't have happened...

There are reasons to and not to use it, for me, I prefer to omit it.

In your application your PCM should kill the fuel pump if theres no IDM signal along with being EFI you have a closed system, fuel will just return to the tank....  Think back to when you ran a carburetor... Not saying it's a must have but there's enough value that a lot of OE's felt it was worth having & we all know how the bean counters chop un-needed over engineered systems...  Then again the bean counters need to think about lawsuits...

Understood.

HI had an electric pump and carb before, I did not have an instance where I needed an oil pressure switch.


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[Cudakiller70]

Thanks for the help everyone!

Took a look at it today, since relay location doesn't matter, just seems easier to put the relay inside of firewall, drivers side, up high. I don't think I should mount the inertia switch there because of e brake. Trunk mounted inertia switch sounds real good and plenty of room for a clean install. Will need to run the ground wire back there with fuel pump wire. Is there a better way?

Prestart prime is important to me. I couldn't figure out bypass with oil pressure switch  , looking at schematics and reading other posts online seems it's possible to back feed starter through OPS. I'm not 100% sure.  Would a switch between 30 and 87 work? Could also be a back up if relay fails. What do you think?

[1 Wild R/T]

I prefer to keep the oil pressure switch & the inertia switch on the low current (control) side of the relay...  Typical Oil pressure switches supply a path to ground but depending on how you want to wire your circuit there is the old Chevy Vega switch which has three prongs, fact is I'm sure it's the one you found reference to since when I tried to find a pin out for it I found this....  However rather than feeding the pump from the switch I'd suggest using it to trigger a relay, socket 86...

Mount your inertia switch near the relay, Probably near the passenger kick panel area...  Ground one side & the other now becomes socket 85...

Fused/circuit breaker equipt Battery lead to 30
Power the pump on 87
87A won't be used...

[Cudakiller70]

This is my attempt at a schematic so please don't laugh and post in joke forum.
Problem I've read and now see in using the OPS (oil pressure switch) with a bypass will back feed through the NC terminal and power starter? Does that seem right to you?

Inertia switch will it work in either location as shown?

[Cudakiller70]

Would this type of bypass work? If so does anyone know where to get that type of switch?

[1 Wild R/T]

Once again I would not put the inertia switch on the pump wiring, I would put it on the control circuit for the relay.... (85) Ford hooked the inertia switch up on the pump circuit in 1985... By 86 that circuit had been redesigned... I'm guessing they knew something....

Same deal on your oil pressure switch, hook it into circuit 86 not circuit 87... 86 is low current & controls circuit 87 which is high current... Hence the 12 ga wire.....

"Problem I've read and now see in using the OPS (oil pressure switch) with a bypass will back feed through the NC terminal and power starter? Does that seem right to you?"

What's gonna feed back? the continuity is with the common leg which has no power, when it receives power either from the starter or the ignition switch is closes the relay contacts & the fuel pump runs... Well, assuming the Inertia switch is closed & the pump is grounded...   

Dummy the circuit up without worrying about neat clean, get it working & poke at it to see if you can make it act up or find ways to improve it...