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  1. #1
    FEP Senior Member Sask84gt's Avatar
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    Default Fuel pump relay wiring help

    Hey all, now that my fuel line is all ran and hooked up I need to wire in my pump using a relay. I bought the painless fuel pump relay kit. It seems pretty straight forward but I do have some questions that hopefully someone who's done this can answer.

    What's the best place to mount the relay? The pump is back by the spare tire well so easiest would be somewhere in the hatch area. Can I run the power wire that goes to battery along the fuel line or is that a no no?

    Should I be running a inertia switch? If so where does that fit into the wiring?

    I need to wire it to a switched 12v source, what's the best wire to tap into. This is my main concern.

    I would like to incorporate a switch or a button that needs to be on before pump will prime. Will that be hooked up to the same wire that runs to the switched source?

    Also car is a 84, did it have a inertia switch somewhere?

    Sorry for all the questions lol electrical is not my cup of tea and I want to be sure I'm doing this right. Here is a pic of the diagram that comes with the wiring kit. Thanks
    https://www.yumpu.com/en/document/re...n-instructions
    Last edited by Sask84gt; 12-04-2020 at 12:01 PM.
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  2. #2
    FEP Supporter Broncojunkie's Avatar
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    I didn't use the Painless setup, but I placed my relay behind the glove box... actually over further toward the passenger side of the box. When I was fighting some electrical gremlins, it was easy to get to for testing/replacing. I ran the wiring through the interior somehow. I believe I drilled a hole somewhere and used a grommet to exit around the rear end, so only a short length was exposed to the elements just before hooking into the external in-line pump (Holley blue).

    I'm curious what others have done. I hate how I routed my fuel lines, so I plan on redoing most of it.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
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  3. #3
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by Broncojunkie View Post
    I didn't use the Painless setup, but I placed my relay behind the glove box... actually over further toward the passenger side of the box. When I was fighting some electrical gremlins, it was easy to get to for testing/replacing. I ran the wiring through the interior somehow. I believe I drilled a hole somewhere and used a grommet to exit around the rear end, so only a short length was exposed to the elements just before hooking into the external in-line pump (Holley blue).

    I'm curious what others have done. I hate how I routed my fuel lines, so I plan on redoing most of it.
    Where did you wire in your 12v switched source? Also, how did you run your fuel line? I ran mine just inside the pinch weld on the passenger side then up into the wheel well behind the plastic liner.
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  4. #4
    FEP Supporter Broncojunkie's Avatar
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    I tapped into a 12v source inside the dash, but I can't recall what it was. It may have been from the fuse box itself using one of those handy fuse adapters. I plan to change things around, since I have a fuel pump cut-off toggle switch on the center console. It comes in handy for carb tuning...like emptying the bowls to adjust floats or rejetting, etc.

    I ran the fuel lines up through the driveshaft/transmission tunnel and up across the firewall. I know that's exactly what you're NOT supposed to do, but again...it was supposed to be temporary anyway. I just haven't got around to changing things. I plan to route it the way you have yours.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller (4cyl build?)
    82gt - working on 408w, c4

  5. #5
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by Broncojunkie View Post
    I tapped into a 12v source inside the dash, but I can't recall what it was. It may have been from the fuse box itself using one of those handy fuse adapters. I plan to change things around, since I have a fuel pump cut-off toggle switch on the center console. It comes in handy for carb tuning...like emptying the bowls to adjust floats or rejetting, etc.

    I ran the fuel lines up through the driveshaft/transmission tunnel and up across the firewall. I know that's exactly what you're NOT supposed to do, but again...it was supposed to be temporary anyway. I just haven't got around to changing things. I plan to route it the way you have yours.
    Ya that's where I was thinking of running my switched source too. Just not sure how to connect it.
    I ran my line above diff and into driveshaft tunnel only as far as where the e-brake cable goes through frame on passenger side. Then curved it and ran it through same whole that cable went through. Actually worked pretty slick.
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  6. #6
    FEP Supporter Broncojunkie's Avatar
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    Pretty sure I used one of these at the fuse box. I wasn't really sure where I wanted it at the time and this was a good temporary fix. No problems so far, but I'm not really sure if this is considered proper.

    Name:  20201204_211618.jpg
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    From now on, on my builds, I'm going to start the wiring process by creating a good 12v switched source....probably with a relay and fuse block so I can use it for everything I add to the car. This includes fuel pump, extra gages, e-fan, aftermarket stereo, etc. The lower-amp stuff can run directly into it while the heavy amp parts can use it for a relay trigger. I'll also probably run a separate 12v power distribution block for heavier gauge wire.... power feed for e-fan, fuel pump, etc.
    Last edited by Broncojunkie; 12-04-2020 at 09:28 PM.
    79 Pace Car - 331, t5
    79 Cobra - working on 351w, t5
    86 coupe - rotbox roller (4cyl build?)
    82gt - working on 408w, c4

  7. #7
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by Broncojunkie View Post
    Pretty sure I used one of these at the fuse box. I wasn't really sure where I wanted it at the time and this was a good temporary fix. No problems so far, but I'm not really sure if this is considered proper.

    Name:  20201204_211618.jpg
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    From now on, on my builds, I'm going to start the wiring process by creating a good 12v switched source....probably with a relay and fuse block so I can use it for everything I add to the car. This includes fuel pump, extra gages, e-fan, aftermarket stereo, etc. The lower-amp stuff can run directly into it while the heavy amp parts can use it for a relay trigger. I'll also probably run a separate 12v power distribution block for heavier gauge wire.... power feed for e-fan, fuel pump, etc.
    Ok, ya that adapter was what I was looking at using. I called a very good local audio store to see if they carried any of those adapters. The guy basically told me they are junk and not to use them. He recommended that I get my 12v switched from the power windows. Not sure which wire to grab from though as there are about 10 going into the window switches. Now I don't know which way to go lol
    Last edited by Sask84gt; 12-05-2020 at 12:34 PM.
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  8. #8
    FEP Senior Member Sask84gt's Avatar
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    So I guess power windows are not a good source for a 12v switched as the window motor does not run when car is starting. Looks like I might just go from ignition wire. Anybody know what color that would be and what the best way to access it is?
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  9. #9
    Moderator wraithracing's Avatar
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    You should be able to find an open fuse location in the fuse panel to use for ignition only power. There is almost always one available in all the Foxes I have worked on. The other option is to use an existing circuit that is ignition only power, but not necessarily being used at start up to make sure you don't overload the circuit. Some quick probing with test light or circuit tester should help you find a good option in the fuse panel. Good Luck!
    ​Trey

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  10. #10
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by wraithracing View Post
    You should be able to find an open fuse location in the fuse panel to use for ignition only power. There is almost always one available in all the Foxes I have worked on. The other option is to use an existing circuit that is ignition only power, but not necessarily being used at start up to make sure you don't overload the circuit. Some quick probing with test light or circuit tester should help you find a good option in the fuse panel. Good Luck!
    Thanks Trey I will look into that. So if there is a open fuse location does a person just run the wire to that fuse spot then pop a fuse in and your good to go?
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  11. #11
    Moderator wraithracing's Avatar
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    Quote Originally Posted by Sask84gt View Post
    Thanks Trey I will look into that. So if there is a open fuse location does a person just run the wire to that fuse spot then pop a fuse in and your good to go?
    Possibly, but generally NO. You will often find and empty fuse socket that has power on the one side, but nothing on the other. The factory didn't wire the opposite side since that fuse location was not needed. You can find the proper wire terminal and run a wire on the backside of the fuse panel to your relay. That would allow you to insert a fuse in that location just like any other circuit. Hope that helps.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
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    1979 Pace Car now 5.0/5 speed
    1982 GT Ongoing RestoModification
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    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Underway
    1984 Capri RS T-top Roller
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  12. #12
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by wraithracing View Post
    Possibly, but generally NO. You will often find and empty fuse socket that has power on the one side, but nothing on the other. The factory didn't wire the opposite side since that fuse location was not needed. You can find the proper wire terminal and run a wire on the backside of the fuse panel to your relay. That would allow you to insert a fuse in that location just like any other circuit. Hope that helps.
    Yup that helps, thanks! This is pretty nerve racking for me lol. Took off the panel to have a look at the fuse box. Uhhgg doesn't look like it's going to be easy to get out to work on.
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  13. #13
    FEP Senior Member Sask84gt's Avatar
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    So after doing a lot of reading and watching of videos it seems that the fuse taps or add a circuts are safe to use as long as your using a relay and not running directly to whatever your powering. That said the add a circut i bought says to connect to the fuse box but not to exceed 10 amps. Does anyone know what a good 12v switched source would be in the fuse panel that doesn't exceed 10 amps? Looking at the fuse box diagram from lmr. https://lmr.com/products/fox-body-mu...panel-diagrams
    It looks like there are 2 fuse spots that are 10 amps. #4 which is for Exterior Lights, Instrument Illumination, Upshift Relay Coil and #18 which is for Carburetor Circuits, Dual Timer Buzzer, Tachometer, Turbo Boost Indicators, Warning Indicators, Low Fuel Warning. Would either of these be good for a 12v switched? There is also a couple that are less than 10 amps which are #13 which is 5 and is for Instrument Illumination and # 2 which is 6 amps and is for Windshield
    Wiper/Washer System.
    Of course I will check with a multimeter when I'm ready but the whole 10 amp max thing is throwing me for a loop lol. Is that just for the item your powering? Meaning I can plug into a 15 or 20 amp fuse spot as long as what I'm running is drawing less than 10 amps? Pretty sure the holley black pulls 4 amps.
    Last edited by Sask84gt; 12-19-2020 at 11:17 AM.
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  14. #14
    FEP Power Member qikgts's Avatar
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    Sask, correct me if I'm wrong, but I think what you are trying to accomplish is to have a power source that is hot in crank and run. If so, the below should help.

    Quote Originally Posted by JACook View Post
    One way to do this would be to use an earlier style starter relay, that has two small posts. On the early
    style relay, the second small post is there to provide a straight 12V ballast bypass to the coil during
    startup. You would tie that to your red/light green 'hot in run' feed.

    The less easy way (or maybe not) is to tie the red/light green and brown/pink wires together, like they
    are on the TFI cars. You might could do that right at the ignition switch connector.
    If using the second method above, at that point the rd/lt gn wire becomes a "true ignition" (hot in crank and run) and you can trigger your relay "coil" with that (so that its on during crank and stays on during run). In your first post you mentioned wanting to wire a switch to turn on the pump so the rd/lt gn is where you would connect the switch after tying the two wires together and power up the relay "coil". To power the pump through the relay output use a fused 12v constant from the battery or whatever constant 12v circuit you want (so long as the circuit you use can handle the amp draw of the pump).

    Hope that helps. If you need more info let me know. This should be pretty simple to resolve.
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  15. #15
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by qikgts View Post
    Sask, correct me if I'm wrong, but I think what you are trying to accomplish is to have a power source that is hot in crank and run. If so, the below should help.



    If using the second method above, at that point the rd/lt gn wire becomes a "true ignition" (hot in crank and run) and you can trigger your relay "coil" with that (so that its on during crank and stays on during run). In your first post you mentioned wanting to wire a switch to turn on the pump so the rd/lt gn is where you would connect the switch after tying the two wires together and power up the relay "coil". To power the pump through the relay output use a fused 12v constant from the battery or whatever constant 12v circuit you want (so long as the circuit you use can handle the amp draw of the pump).

    Hope that helps. If you need more info let me know. This should be pretty simple to resolve.
    qikgts, thanks for the reply. Ya I think that's what I'm looking for although the instructions in the painless relay kit just say 12v switched source. Right now I have the relay mounted in the spare tire well. I have the correct wire running to pump and the power wire running to a circut breaker located in the engine bay. Other side is ran to the battery. All grounds In place. Now i just need to run the last wire to a 12v switched source. I want to add a switch in between this to be able to switch the pump off even though the key is in and ignition is on. I was hoping I could use a fuse tap( add a circut) to tap into a switched source from fuse box instead of cutting into wires. Hope I made sense lol
    Last edited by Sask84gt; 12-19-2020 at 10:51 PM.
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  16. #16
    FEP Power Member qikgts's Avatar
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    12v switched is certainly not true ignition. Some people miss the hot in crank and run detail and never think twice about it, unless they're powering an ignition box or fuel pump and it doesn't work. Then the difference becomes clear.

    If you want to use the switch to trigger the relay, no harm no foul and you can do that in the fuse box easily with that fuse tap deal. You can supply the switch with constant 12v from any fuse that is hot all the time. You'll just need to remember that's it's always going to be energized, key on or off.

    Personally I think it's better to make and use that "true ignition" circuit to feed the switch so you'll never burn up the pump or kill the battery by accidently leaving the switch on.
    '85 GT

  17. #17
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by qikgts View Post
    12v switched is certainly not true ignition. Some people miss the hot in crank and run detail and never think twice about it, unless they're powering an ignition box or fuel pump and it doesn't work. Then the difference becomes clear.

    If you want to use the switch to trigger the relay, no harm no foul and you can do that in the fuse box easily with that fuse tap deal. You can supply the switch with constant 12v from any fuse that is hot all the time. You'll just need to remember that's it's always going to be energized, key on or off.

    Personally I think it's better to make and use that "true ignition" circuit to feed the switch so you'll never burn up the pump or kill the battery by accidently leaving the switch on.

    qikgts, where is the best place to locate that wire and tie in?
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  18. #18
    FEP Power Member qikgts's Avatar
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    Name:  83-86 fuse panel.JPG
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    Fuse 16 looks good to me. Again, this fuse will be a constant 12v supply and using that fuse tap adapter broncojunkie posted up above is fine for this.

    So as I said above, you'll have to be aware that leaving your switch on could kill the battery or pump.

    If using that adapter, you'll replace the 20 amp fuse that's in the box now with the adapter and reinstall the 20 amp fuse into the adapter to protect the original circuit as it was before. (That will be duplicating the fuse in the box.) Then you can install a smaller amp fuse, like a 3 or 5 amp, into the slot that will feed the "wire" coming off the adapter.

    Credit goes to LMR for providing that great fuse box image.
    Last edited by qikgts; 12-26-2020 at 09:27 PM.
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  19. #19
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by qikgts View Post
    Name:  83-86 fuse panel.JPG
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    Fuse 16 looks good to me. Again, this fuse will be a constant 12v supply and using that fuse tap adapter broncojunkie posted up above is fine for this.

    So as I said above, you'll have to be aware that leaving your switch on could kill the battery or pump.

    If using that adapter, you'll replace the 20 amp fuse that's in the box now with the adapter and reinstall the 20 amp fuse into the adapter to protect the original circuit as it was before. (That will be duplicating the fuse in the box.) Then you can install a smaller amp fuse, like a 3 or 5 amp, into the slot that will feed the "wire" coming off the adapter.

    Credit goes to LMR for providing that great fuse box image.
    Thanks, I wont be tapping into a constant 12v supply because I just know the switch will be left on at some point. I'm going to do some probing with a multimeter next week and see what I can find. Theres got to be a fuse that has 12v on crank and run but nothing when key isn't in.
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  20. #20
    FEP Senior Member Sask84gt's Avatar
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    Broncojunkie, you think you could have a look at your fuse panel for me and see which one you tapped into?
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  21. #21
    FEP Power Member qikgts's Avatar
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    Quote Originally Posted by Sask84gt View Post
    I'm going to do some probing with a multimeter next week and see what I can find. Theres got to be a fuse that has 12v on crank and run but nothing when key isn't in.
    I never say never when someone is willing to put a multimeter to use. However, I'm pretty sure you'll come up empty in the fuse box and you'll wind up needing to do one of the two things I quoted above to get the hot in crank and run unless of course your car isn't like all the others.
    '85 GT

  22. #22
    FEP Senior Member Sask84gt's Avatar
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    Quote Originally Posted by qikgts View Post
    I never say never when someone is willing to put a multimeter to use. However, I'm pretty sure you'll come up empty in the fuse box and you'll wind up needing to do one of the two things I quoted above to get the hot in crank and run unless of course your car isn't like all the others.
    Pretty sure my car is like all the others and I don't doubt what your saying at all. I'm new to all this and really have no first hand experience. I'm learning from reading online and from what help I get from here.

    So if I can't find a hot in crank and run in the fuse box where is the best place to locate the red and light green wire and the brown and pink? Steering column? Drivers side kick panel area? Starting to really regret not changing timing cover to support a mechanical pump when engine was out. Took advice I shouldn't of.
    Last edited by Sask84gt; 12-27-2020 at 02:01 PM.
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  23. #23
    FEP Power Member qikgts's Avatar
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    If it was me doing this, I would do it near the ignition switch connector. At the same place where I'd need to tie the red/light green and brown/pink wires together. Into that that exact, new splice is right where I'd put my fuse holder.

    Hopefully the image is not confusing. I wanted to delete it but it stayed with the post.

    The reason why it may be confusing is it doesn't show the continuation of the brown/pink wire "after the splice". The reason why I made the image that way is that I believe it dead ends in the harness and depending on where you did the splice, the excess would not need to be reconnected.

    That said, I've read that some cars may not even have the brown/pink present. If that was the case you'd need to install it in the ignition switch connector and then do the splice.

    The link below is generic to Fox body cars but I think the location of the pin is accurate.

    http://www.veryuseful.com/mustang/te...itchWiring.gif

    All of this assumes (you know what that means... lol) that your car wasn't fuel injected from the factory. If it was, then I've been wasting bandwidth and our time as the wires may already be spliced from the factory. Oy vey.... Sometimes I wonder about me... lol
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    Last edited by qikgts; 12-27-2020 at 02:55 PM.
    '85 GT

  24. #24
    FEP Senior Member Sask84gt's Avatar
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    Ok, so help me understand something. I can understand why ideally you would want hot In crank for a fuel pump but wouldn't just a hot when key is in and ignition is turned on work also? I mean you would put key in and turn ignition on which would send fuel to the carb then when you turned it over there would be fuel In carb to start car which in turn you would release leaving car in run mode which would continue to run pump.
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  25. #25
    FEP Power Member qikgts's Avatar
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    I think that makes perfect sense. Maybe hot in run isn't needed at all with a carb.

    Thinking more about it, the only time it may matter is if there is a long crank time and the bowl goes dry from pumping the throttle. And even then, I guess it's not a big deal to just stop cranking and let the bowl fill again.

    If you run it switched power can you report how it works out? I'm always open to learning something.

    Another edit to a post in this thread.... Jeez.... : I just found this link and there is no mention of using a hot in crank and run. I do like the oil pressure switch they used though.

    https://www.hotrod.com/articles/safe...l-pump-wiring/
    Last edited by qikgts; 12-27-2020 at 06:26 PM.
    '85 GT

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