Any reason not to let the Holley run the fuel pump?

I am posting this here because the Cobra forum gets way more traffic than the truck and this is a universal engine wiring question. I have a Holley Terminator X and it can control most accessories. I have it running the cooling fan but I left the fuel pump on the RF harness. When you turn the key to the run position the pump comes on and stays on. I am pretty sure the Holley powers it (like my Coyote) where as it primes the pump but doesn't run it continuously until the engine is running. I have been unplugging the pump while programing and fiddling with software but am now thinking about whether to change it.

The upside is the fuse for the fuel pump is in the RF fuse box. The fuse for the Holley is under the transmission tunnel, accessible only if the truck is on a lift. So as I see it my options are as follows:

1. Leave it, if I turn the key to mess with the engine setup the pump runs in the background. It's annoying, runs down the battery but otherwise not causing any issues.

2. Directly wire the Holley to the fuel pump. Upside is the limited running, but if the fuse goes it's kind of a pain and probably can't be fixed by the side road.

3. Run the Holley power wire to the RF fuse box and replace the fuel pump relay trigger voltage with the Holley 12 volt wire. With this arrangement if the fuse goes it's where you would expect it to be and it's labeled. This is the least "clean" option because I have to run a single wire and cut into the fuse box. I am also sort of double relayed and double fused. The odds of blowing the Holley fuse while it's only powering a relay is incredibly low but if it happened would take someone a while to figure it out.

All three use the inertia switch ground so rollover protection stays in place.


What would you do? I'm all ears


**Edit - Adding that the Holley Terminator comes with an optional fused 12v direct to fuel pump power wire**

Blitzboy54, I’m at the same decision point with my roadster since I just converted from carb to sniper 2. Isn’t the Holley fuel pump wire a ground trigger? The sniper 2 blue fuel pump wire is a ground trigger. The fuel pump relay in the RF roadster harness is a ground triggered relay. If your Holley fuel pump wire and your RF harness are the same, there’s an option 4-wire the Holley fuel pump trigger to the chassis ground side of the inertia switch. In other words, disconnect the inertia switch chassis ground wire from the chassis and wire it to the Holley fuel pump ground trigger wire (blue for sniper 2). I’ve added blue text to show this on the attached RF harness diagram. I plan to make this mod on my roadster when I get around to cleaning up the engine harness looms-for now it runs and runs like yours. thoughts?Attachment 228271

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Originally Posted by BUDFIVE

Blitzboy54, I’m at the same decision point with my roadster since I just converted from carb to sniper 2. Isn’t the Holley fuel pump wire a ground trigger? The sniper 2 blue fuel pump wire is a ground trigger. The fuel pump relay in the RF roadster harness is a ground triggered relay. If your Holley fuel pump wire and your RF harness are the same, there’s an option 4-wire the Holley fuel pump trigger to the chassis ground side of the inertia switch. In other words, disconnect the inertia switch chassis ground wire from the chassis and wire it to the Holley fuel pump ground trigger wire (blue for sniper 2). I’ve added blue text to show this on the attached RF harness diagram. I plan to make this mod on my roadster when I get around to cleaning up the engine harness looms-for now it runs and runs like yours. thoughts?Attachment 228271

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Yes on the Sniper about it being a ground trigger. On the Terminator it's a 12 gauge "direct to pump" 12v power wire. That's why in my case I can leave the inertia switch alone. When I had a Sniper on a previous build I used it to run the pump and had to put the inertia switch inline so it would still be protected.

I understand, yours is more like the sniper 2 main harness with a fuel pump relay (558-191) where the blue wire is +12v direct to the fuel pump. I’m using the blue wire from the 16 pin connector which is pre-relay and a ground trigger. Sorry for the diversion.

I'm in the same boat. I have the fuel pump currently wired the RF way, but would like the Terminator X to control things so it does the priming, then only runs the pump when RPM are sensed.

ChatGPT seems to think you can use the Holley software and change a different ground output to "fuel pump". I'm not sure. I see no mention of this when I Google it.

I'll need to check into that, but the backup is to use the green +12v to trigger a relay to ground the current RF circuit. That way the inertia switch will still work.

I already wired in an on/off switch into that RF ground that is on my trans tunnel so I could manually turn the pump off so it's not annoyingly running all the time. When I change things over to the Terminator X that'll still be useful as a theft deterrent, I suppose

I've done it both ways. Both are controlled by Holley and both protected with the inertia switch. My HP is + controlled to the pump relay and the Sniper is - controlled to the pump. Both work just fine. I also have fuses located in accessible areas.
Attachment 228285 Attachment 228286

I have my Terminator wired so that it controls the fuel pump. You've guessed correctly; the Terminator provides a 5-second prime & then shuts off if you haven't started the car.

I de-pinned the RF fuel pump wire from the feed side of the RF rear harness, and put the Terminator direct to fuel pump power wire in its place (in effect, eliminating the RF fuel circuit entirely). Then I cut the inertia switch out of the RF circuitry and wired it in-line with the Terminator direct to fuel pump power wire. I felt comfortable doing this because my Terminator documentation said the fuel pump power was a 12A feed, and the part number on the inertia switch revealed it was rated to 15A. If you can't verify the inertia switch current capacity, you can break into the relay wiring so that the inertia switch is on the trigger side of the circuit rather than the feed side.



John

I have sniper2 control the pump as designed. But the suggestion is to add a switch under dash to break the inertia switch line. That way when you are doing software or just need the ignition on, the pump will not run. Also acts as a hidden anti-theft although most would just tow the car not try to drive it.

Another thought given your component layout: You could break into the Terminator fuel pump relay trigger & use that to substitute for the RF fuel pump relay trigger. Doing so would eliminate your double relay, double fuse situation.


John

Maybe I am missing something here but it sounds like you can wire the Holley trigger to the RF pump circuit just like you do the Coyote. When you turn the key, the Coyote software initiates the fuel pump circuit which uses the RF relay and wiring to the pump but ultimately the Coyote software is driving the bus. Sounds like you can do the same thing with the Holley software?

Keep in mind that the inertia switch, if installed per the RF instructions, is in-line with the ground side of the RF fuel pump relay. If you bypass the RF fuel pump relay, the inertia switch does nothing for you unless you move it into the "new" fuel pump circuit. You can wire in-line with the ground on the fuel pump rather than at the relay, and it will function as intended regardless of the up-stream option you elect to use.

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Originally Posted by Papa

Keep in mind that the inertia switch, if installed per the RF instructions, is in-line with the ground side of the RF fuel pump relay. If you bypass the RF fuel pump relay, the inertia switch does nothing for you unless you move it into the "new" fuel pump circuit. You can wire in-line with the ground on the fuel pump rather than at the relay, and it will function as intended regardless of the up-stream option you elect to use.

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In all my above scenarios I am replacing the only either the 12v power source or the 12v relay trigger. The ground side of the cirucut is unchanged. Therefor any break in it (ie the inertia switch) will stop the pump.

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Originally Posted by PNWTim

Maybe I am missing something here but it sounds like you can wire the Holley trigger to the RF pump circuit just like you do the Coyote. When you turn the key, the Coyote software initiates the fuel pump circuit which uses the RF relay and wiring to the pump but ultimately the Coyote software is driving the bus. Sounds like you can do the same thing with the Holley software?

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I can, that is essentially option 2. The location of the fuse was my hesitation. this would be the easiest solution by far. The Coyote comes with it's own fuse panel that sits in the engine bay. With the 35 pickup the fuse for the Holley is sitting right next to the transmission. It could not be replaced without a lift to access it from underneath.

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Originally Posted by phileas_fogg

Another thought given your component layout: You could break into the Terminator fuel pump relay trigger & use that to substitute for the RF fuel pump relay trigger. Doing so would eliminate your double relay, double fuse situation.


John

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This is a very good idea. I'll take some measurements tonight. the relay is right next to the fuse. Should be pretty straight forward.

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Originally Posted by Blitzboy54

In all my above scenarios I am replacing the only either the 12v power source or the 12v relay trigger. The ground side of the cirucut is unchanged. Therefor any break in it (ie the inertia switch) will stop the pump.

I can, that is essentially option 2. The location of the fuse was my hesitation. this would be the easiest solution by far. The Coyote comes with it's own fuse panel that sits in the engine bay. With the 35 pickup the fuse for the Holley is sitting right next to the transmission. It could not be replaced without a lift to access it from underneath.

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Sorry if I'm not understanding, but the ground to the pump is not affected by the inertia switch. So, for your option #2, if you run power direct to the pump, the inertia switch will not interrupt the pump, which is chassis grounded in the RF harness. Unless you meant to run the power to the RF fuel pump relay on the feed vs. trigger, which would do the trick and keep the inertia switch in the loop.

Dave

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Originally Posted by Papa

Sorry if I'm not understanding, but the ground to the pump is not affected by the inertia switch. So, for your option #2, if you run power direct to the pump, the inertia switch will not interrupt the pump, which is chassis grounded in the RF harness. Unless you meant to run the power to the RF fuel pump relay on the feed vs. trigger, which would do the trick and keep the inertia switch in the loop.

Dave

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No that's me being a dope. You are 100% right. I only have the switch protection if I tie it into the RF harness relay. If I move to directly power it from the Holley I have to move the switch. I had it in my head the inertia switch was tied to the ground coming off the pump. It is not, it is coming off the ground to the relay.

"Better to remain silent and be thought a fool than to speak and remove all doubt" seem relevant here.


Thanks Papa

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Originally Posted by Blitzboy54

No that's me being a dope. You are 100% right. I only have the switch protection if I tie it into the RF harness relay. If I move to directly power it from the Holley I have to move the switch. I had it in my head the inertia switch was tied to the ground coming off the pump. It is not, it is coming off the ground to the relay.

"Better to remain silent and be thought a fool than to speak and remove all doubt" seem relevant here.


Thanks Papa

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No worries. Better to ask questions than to make assumptions.

Dave

Hey guys not trying to hijack this thread, but with the Holley Sniper 2.0 and the PDM, do you need an inertia switch? I just finished rewiring my fuel pump and fan circuits because I failed to research how the PDM really worked. Now I have that done and I'm debating on do I need the inertia switch. This thread has peaked my interest even more...

According to my research with AI, the fuel pump should shut off if the RPM signinal is lost. Looking for feedback, because now is the time to add one I guess. I would put it on the (+) wire from the pump to the PDM. Unfortunately, that would put it behind the dash and would have limited access...

Thanks!

The inertia switch will not handle the amp load of the high output pumps being used now, it needs to be installed on the switch leg side of the fuel pump relay. I have no answer about if the PDM shuts off the fuel pump, but it ISN"T an inertia switch, and you can be in an accident and the engine continue to run. It's such a simple safety device to install, I see NO reason not to use it.

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Originally Posted by BUDFIVE

Blitzboy54, I’m at the same decision point with my roadster since I just converted from carb to sniper 2. Isn’t the Holley fuel pump wire a ground trigger? The sniper 2 blue fuel pump wire is a ground trigger. The fuel pump relay in the RF roadster harness is a ground triggered relay. If your Holley fuel pump wire and your RF harness are the same, there’s an option 4-wire the Holley fuel pump trigger to the chassis ground side of the inertia switch. In other words, disconnect the inertia switch chassis ground wire from the chassis and wire it to the Holley fuel pump ground trigger wire (blue for sniper 2). I’ve added blue text to show this on the attached RF harness diagram. I plan to make this mod on my roadster when I get around to cleaning up the engine harness looms-for now it runs and runs like yours. thoughts?Attachment 228271

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The location you are showing is the main chassis ground for the entire harness. You don't want to tie the Holley there, but rather to the chassis side (right side) of the inertia switch shown in the diagram you posted.

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Originally Posted by Papa

The location you are showing is the main chassis ground for the entire harness. You don't want to tie the Holley there, but rather to the chassis side (right side) of the inertia switch shown in the diagram you posted.

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Papa, thanks for catching this, I didn’t notice the branch on that wire in the diagram. You’re correct the holley ground trigger should only be connected to the ground side (right) of the inertia switch.