Fuel pump 10g upgrade keeping the Inertia

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I saw a few posts here that a new harness was ran for the bigger pumps like 10g wire to the inertia switch to maintain that safety system. What exactly did you do with the pigtail or where did the relay switched and 10g power land?

I finally have some time to run my Aeromotive harness from my walbro Hellcat 525 pump In my fancy ATP tank.
 
Required said:
I saw a few posts here that a new harness was ran for the bigger pumps like 10g wire to the inertia switch to maintain that safety system. What exactly did you do with the pigtail or where did the relay switched and 10g power land?

I finally have some time to run my Aeromotive harness from my walbro Hellcat 525 pump In my fancy ATP tank.
Click to expand...

On my black truck I ran the inertia switch on the ground side.
 
Required said:
Collisions can cause unexpected grounds, I’m now questioning whether the factory inertia switch will support a 30amp circuit.
Click to expand...

Absolutely, but which is worse, melting that inertia switch pigtail or the chance of a ground? I am pretty sure those wires are tiny, but it was a long time ago when I was wiring it up.
 
I also question the ability of the switch to handle the current necessary to run a big pump. Might be best to use a relay with the inertia switch controlling it or use an oil pressure switch like GM.
 
oilwell1415 said:
I also question the ability of the switch to handle the current necessary to run a big pump. Might be best to use a relay with the inertia switch controlling it or use an oil pressure switch like GM.
Click to expand...
Hmn, coil current is a good idea. No pump power through the switch. Just relay activation…
 
Right you'd really want to drive a relay with the inertia switch. I didn't use the inertia switch when I wired mine. I really should.

On the factory system, is the inertia switch actually wired to the pumps, or is it incorporated in the relay? If it's to the relay, then I'm fine since I just use the factory relay circuit to drive a bigger relay.
 
Revisiting this topic... Looking at running larger wires to the pump and using the factory pump relay as a switch to control a secondary relay to power the pump. Looking at the diagram above, I just need to use the rear tank (no front tank anymore) Br/W and Org wires to switch a relay that will have the new power/ground wires to power the pump. This would keep the factory circuitry in place, but better power the pump. Am I looking at this correct?

I was planning to run 8ga wire based on charts showing 20amps over 15-20', but that seems way overkill as well. What have you all run in the past? Seems silly considering a 40amp relay has 12ga wire and the factory pump wires in the tank are likely 16-18 ga.

I will likely upgrade to the Holley 340 intake fuel hat assembly in the future, but right now I'm just running a Quantum 340 pump in the factory assembly. Maybe this is all a waste of time as well. 🤷‍♂️
 
core-rider said:
Revisiting this topic... Looking at running larger wires to the pump and using the factory pump relay as a switch to control a secondary relay to power the pump. Looking at the diagram above, I just need to use the rear tank (no front tank anymore) Br/W and Org wires to switch a relay that will have the new power/ground wires to power the pump. This would keep the factory circuitry in place, but better power the pump. Am I looking at this correct?

I was planning to run 8ga wire based on charts showing 20amps over 15-20', but that seems way overkill as well. What have you all run in the past? Seems silly considering a 40amp relay has 12ga wire and the factory pump wires in the tank are likely 16-18 ga.

I will likely upgrade to the Holley 340 intake fuel hat assembly in the future, but right now I'm just running a Quantum 340 pump in the factory assembly. Maybe this is all a waste of time as well. 🤷‍♂️
Click to expand...
Yes, just put the control side of the relay between the Br/W and O wires.

8ga wire doesn't seem like that much of a stretch. I'm sure it would be safe with smaller wire, but the voltage drop may be excessive. When in doubt, always go with the larger wire.
 
core-rider said:
Revisiting this topic... Looking at running larger wires to the pump and using the factory pump relay as a switch to control a secondary relay to power the pump. Looking at the diagram above, I just need to use the rear tank (no front tank anymore) Br/W and Org wires to switch a relay that will have the new power/ground wires to power the pump. This would keep the factory circuitry in place, but better power the pump. Am I looking at this correct?

I was planning to run 8ga wire based on charts showing 20amps over 15-20', but that seems way overkill as well. What have you all run in the past? Seems silly considering a 40amp relay has 12ga wire and the factory pump wires in the tank are likely 16-18 ga.

I will likely upgrade to the Holley 340 intake fuel hat assembly in the future, but right now I'm just running a Quantum 340 pump in the factory assembly. Maybe this is all a waste of time as well. 🤷‍♂️
Click to expand...

When I first got the black truck running I used 12ga wire to my big Weldon external fuel pump. Later on when I was upgrading to a PDM and was cleaning up the wires I saw signs that the wire had been getting hot so I swapped to 10 gauge. Once I was able to log amp draw I saw that steady state was around 13A, but on startup it was much, much higher. I'm trying to understand how you'll have 15 to 20' of wire length? Where is the fuel pump power source? Are you coming right off the battery?
 
Raymond_B said:
When I first got the black truck running I used 12ga wire to my big Weldon external fuel pump. Later on when I was upgrading to a PDM and was cleaning up the wires I saw signs that the wire had been getting hot so I swapped to 10 gauge. Once I was able to log amp draw I saw that steady state was around 13A, but on startup it was much, much higher. I'm trying to understand how you'll have 15 to 20' of wire length? Where is the fuel pump power source? Are you coming right off the battery?
Click to expand...
I was planning to either got to the battery and put a fuse or circuit breaker in-line, or come off the factory fuse panel if it wasn't too much trouble. I was thinking 15-20' was more than enough wire to reach the battery and go all the way the fuel tank once it goes down/around/through everything.
 
I’d stick with 10–12ga. A single 340–525 lph pump is gonna pull somewhere around 18–20 amps once it’s up and running at 50–60 psi, and they’re totally fine with a little voltage drop. Those wire‑size charts everyone quotes are built around zero voltage drop, which just isn’t real‑world.
If you’re at 14v at the alternator, quick math at 20 amps says:

12ga over a 15-20ft might drop around 1.3v
10ga is more like 0.8v

Neither of those numbers is enough to noticeably hurt pump output unless the pump is sized right at the ragged edge of what the combo needs. A healthy single pump has plenty of cushion.
If you’re only feeding one pump and the total wire length isn’t insane, 10–12ga is plenty. People jump straight to 8ga because the charts assume worst‑case length and load, but in the real world you oversize the pump anyway. It only becomes a problem when you’re truly on the edge of pump capacity.

What pump are you running? What psi under boost (i'm assuming 1:1 regulator)? What hp are you at OR do you know how much lph you need?
 
Running a Quantum 340 now, but thinking about eventually moving to the Holley on-tank assembly which also uses a 340 pump. Could also mount someone larger to it in the future. I’m seeing a fuel pressure drop under boost with hard acceleration and thinking it’s either fuel starving the pump or lack of power. Likely fuel starving because under mild acceleration with same boost numbers I don’t see the fuel pressure drop the same. Somewhere in the 400-450rwhp range. Just running 93 octane… I think I have enough pump.

I was using this wire calculator… Wire size calc

I’m going off worst case of 20’ wire, but even at 15’ it still says 8ga. I’m likely being too careful, but last thing I want to do is watch my truck burning on the side of the road!
 
There are a lot of things that will have a 30 year old truck burning on the side of the road. Using 10 or 12 gauge wire in this application is a long way down that list.

When I use the calculator at that link it automatically sizes the wire for a 2% drop. That is unrealistic and likely why it's showing you such big wire. Another variable that may or may not be accounted for in that calculator is wire quality. All electric wire is not created equal. A good quality wire will perform better than the cheap China wire you get at the parts store. The copper will be of higher quality and the wire will be finer strands.
 
the fuse is protecting you against fire.. the wire sizing question is only about voltage drop. The pump is just going to put out just slightly less at 13v, but very common. Real street has a good test blog below. All done at 13.2v. Use an AI or other calculators to check.

A 340 is enough for like 900hp on gas, so yea, not the pump or the voltage problem. wire size is not the pressure drop issue.

that 340 in the stock canister is the issue. I use a radium surge tank with a small intank lift pump to solve that.
Options I'm aware of on the fuel starving:
1. Surge tank setup
2. holley drop in (i think these are front tank only)
3. or make your own drop using an 88 f-150 hanger assembly and holley hydramat.
4. ATP tank

 
rusty_408 said:
the fuse is protecting you against fire.. the wire sizing question is only about voltage drop. The pump is just going to put out just slightly less at 13v, but very common. Real street has a good test blog below. All done at 13.2v. Use an AI or other calculators to check.

A 340 is enough for like 900hp on gas, so yea, not the pump or the voltage problem. wire size is not the pressure drop issue.

that 340 in the stock canister is the issue. I use a radium surge tank with a small intank lift pump to solve that.
Options I'm aware of on the fuel starving:
1. Surge tank setup
2. holley drop in (i think these are front tank only)
3. or make your own drop using an 88 f-150 hanger assembly and holley hydramat.
4. ATP tank

Click to expand...
Holley offers drop in kits for the rear tanks now on short and long bed applications. I believe the stock canister is being sucked dry before fuel can refill it and that's why I see pressure drop. Wondering if cutting holes in the canister would help, but at that point I might as well just replace it with the Holley unit.

APT tank would be a great answer if they weren't so dang proud of them! 🤑
 
oilwell1415 said:
There are a lot of things that will have a 30 year old truck burning on the side of the road. Using 10 or 12 gauge wire in this application is a long way down that list.

When I use the calculator at that link it automatically sizes the wire for a 2% drop. That is unrealistic and likely why it's showing you such big wire. Another variable that may or may not be accounted for in that calculator is wire quality. All electric wire is not created equal. A good quality wire will perform better than the cheap China wire you get at the parts store. The copper will be of higher quality and the wire will be finer strands.
Click to expand...
I was thinking the same about 2% drop. I will use good quality OFC copper wire used for stereo applications.
 
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