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How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
LTX and LSXPutting LT1s, LS1s, and their variants into Third Gens is becoming more popular. This board is for those who are doing and have done the swaps so they can discuss all of their technical aspects including repairs, swap info, and performance upgrades.
How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Seen a lot of threads recently with people confused how to wire a 4th gen fuel tank into a 3rd gen. I'm going to post a few tips that will help people get through it.
The information presented here is aimed at cars equipped with factory in-tank electric pumps. I am not familiar with earlier 3rd gens with mechanical fuel pumps. Somebody else can add information for those earlier cars if they want, but I assume the entire fuel system has to be built from scratch.
Overview of Stock 3rd Gen Wiring
Cars with a factory in-tank electric fuel pump have a fuel pump relay located on driver side firewall near the brake booster. The electrical design of the fuel system varies slightly depending what engine is in the car (V6, TBI V8, TPI V8) but all have common wire colors at the relay,
The two thin wires, DK GRN / WHT: Relay Control BLK / WHT: Chassis Ground for relay control
The two thick wires, ORG: Fused power from Battery B+ TAN / WHT: Fuel pump (14 AWG)
After the TAN/WHT wire leaves the fuel pump relay, it goes to a firewall pass-thru (C100) into the interior of the car, travels under the rocker cover next to driver seat, and goes to another firewall pass-thru (C313) located behind the rear seat. Wire colors and functions at C313 are,
Interior Side (hard wired): BLK: Chassis ground (14 AWG) PNK: Fuel gauge TAN / WHT: Fuel pump power (14 AWG)
Exterior Side with Weather-Pack connector:
Pin A: BLK, Fuel Pump & Fuel Gauge ground (14 AWG)
Pin B: PNK, Fuel Gauge
Pin C: TAN, Fuel Pump power (14 AWG)
The C313 pass-thru is a custom low-profile Weather-Pack connector and there is no aftermarket replacement part. Wires on the interior side of the car are permanently attached to the connector and cannot be de-pinned or removed. Do not cut the wires unless you have a really good plan up your sleeve because you cannot replace it unless you pull another out of a junkyard. The connector is also riveted to the sheet metal of the car.
Below is a picture of C313 pass-thru bulkhead removed from car. Rivets have been popped and wires cut to remove it from car. I was stupid and removed mine when I didn't know what else to do trying to run a Hotwire kit. Don't be like me, be smarter and leave it in the car.
The mating connector on the outside is a Weather-Pack style, part number 12020829. Compatible terminals and seals are listed below. Maximum continuous current rating of a Weather-Pack terminal is 20 Amp which is higher than the rating of the stock 14 AWG wire at 14 Amp maximum continuous.
How Much Pump Will Stock Wiring Support?
The stock fuel system has a variety of components and connectors, each with its own current rating.
The stock wiring is designed for a Walbro 190 L/hr pump and can operate up to a 255 L/hr pump. However, the system design results in a lot of voltage drop due to the many connections in system, and those voltage losses cause the pump to operate at a lower flow rate. I don't know how much voltage drop is in the system, never measured it. But I do know the 255 pump will support more horsepower if that voltage drop is eliminated and that's what a Hotwire kit does. More about Hotwire kits later.
Prepping a 4th Gen Fuel Tank
The 4th gen fuel tank is not plug and play with 3rd gen body harness, and the fuel sender is not compatible with the stock fuel gauge. Some preparation is needed to make the fuel tank usable.
Swapping Fuel Sender: The 4th gen tank has a 40-250 Ohm fuel level sender that is incompatible with the stock fuel gauge. It causes the gauge needle sweep to move out of range of what the gauge can display. The fuel gauge will spend a lot of time above the Full mark as fuel is used up, and then the needle will drop quickly and you will run out of gas when the gauge reads somewhere between 1/4 to 1/2 tank. The fuel gauge will never read Empty unless the sender goes to 0 Ohm. And the sender has to be 0-90 Ohm if you want the full range of sweep from Empty to Full.
The solution is to change out the resistor card inside the fuel tank with a 0-90 Ohm version, AC Delco part number 25319676 (also sold as SK1083). All you want is the resistor board, the rest of the kit will be discarded. No wires need to be cut, no soldering is involved, no zip ties to hold anything, and you keep the 4th gen float and rod. This is a direct parts swap as if GM built it that way.
Step 1: Take your new AC Delco 25319676 out of the box and confirm with a multi-meter that the resistor is actually 0-90 Ohm. Sometimes the wrong parts are shipped in the box and you want to make sure your time is not wasted.
Step 2: Separate the purple wires from the connector. Remove the terminal keeper from back of connector and remove the wires with a Metri-Pack 150 terminal removal tool.
Step 3: Check to see if the float assembly mounts up to your fuel bucket. It might, or it might not depending what generation of design you have. If it does fit then slap the pump assembly together and you're done. If it doesn't fit then go on to the next step.
Step 4: If the new float assembly didn't fit, then remove the resistor card itself and move it over to the stock 4th gen float assembly that does fit. Remove the retainer that keeps the resistor card located, and then slip the card out of the holder. Do the same with the stock float assembly and then install the new 0-90 Ohm resistor card. Finish re-assembling the pump assembly and you're done.
Vent Valve: Eliminating wiring to the solenoid vent valve will cause the valve to remain open at all times and the tank will vent through the charcoal canister. Strip all these wires out of the harness.
Pressure Sensor: No wiring is needed to the air pressure sensor after disabling the solenoid vent valve. Strip all these wires out of the harness. Although the sensor could be used to monitor tank pressure if your ECM has inputs to read the sensor, such as Holley EFI.
Fuel Module: The remaining wires are for the fuel pump assembly that houses the fuel pump and fuel level sender. The tank bulkhead uses a Metri-Pack 150 style connector rated at 14A maximum continuous. This handles up to a Walbro 255 L/hr pump typical with most LS swaps. Wire pinouts are,
Fuel systems with larger 340 L/hr pump should change out the bulkhead connector to a GT 280 style connector rated at 25A maximum continuous. Pinouts are not standardized as this was not a factory option. Racetronix sells a pump module and Hotwire kit specifically for the 340 pump. If you want to try to swap out the bulkhead connector on your own then part numbers are shown in this thread, https://www.thirdgen.org/forums/ltx-...lectrical.html
The connector that plugs into the 4th gen body harness is the wrong style to plug into the 3rd gen body harness. You'll need to remove it and replace with an appropriate connector based on how you choose to power your fuel pump. And that is the next topic matter to discuss...
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Mating To Stock 3rd Gen Wiring
If you want to mate a 4th gen fuel tank to stock 3rd gen body wiring then just match like function with like function. Reference pinouts and connector part number given earlier in this thread. The 3rd gen body harness has 3 wires while the 4th gen tank has 4 wires. This is also the case with stock 3rd gen fuel tank but the solution is hidden inside the tank where you can't see it. To go from 4 wires to 3 wires,
Method A: Splice together the Fuel Pump Ground and Fuel Sender Ground wires and run the wire to 'Pin A' of the C313 connector. This is how it's done in a stock 3rd gen.
Method B: Run the Fuel Sender Ground wire into the factory location at 'Pin A' of the C313 connector. Ground the Fuel Pump Ground wire to the body of the car behind the rear seat. Make sure this is a really good metal to metal ground, cleaned of all paint and dirt. Most people will put a ring terminal directly to the body of the car. The better method is to weld a stainless threaded boss to the body and attach the ring terminal to the boss. You can get a boss from Caterpillar, part number 175-1540 (stainless, M10 thread, 1" tall).
Method C: See Post #4. This method will double the current capacity that can be fed through the C313 connector.
Custom harness built using Method A. If you want one like this then PM me and I can set you up.
Example of stainless ground boss welded to firewall behind rear seat, used with Method B.
Fuel Pump Relay: The other thing you need to do is control the fuel pump relay with your engine ECM. This is very simple. If your ECM has a +12V source that is used to turn the fuel pump on/off (GM and Holley ECM's operate this way), then run that wire to the GRN/WHT wire location in the stock relay. Make sure the stock BLK/WHT wire still has a path to ground. If you are even more adventurous, then you can remove the stock relay entirely from the car and use your ECM to directly operate the Racetronix relay by tying into the stock TAN/WHT wire that passes into the interior of the car.
If your ECM has a sinking driver that switches to ground to turn fuel pump on/off, then run that wire to the BLK/WHT wire location in the stock relay. And you'll need to change the GRN/WHT wire so that it gets +12V from a fused power source when the key switch is turned on. I'm not sure what ECM would be configured this way but it's maybe a possibility with lower cost platforms since sinking drivers are less expensive than +12V sourcing drivers.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Racetronix Hotwire Kit
The Racetronix Hotwire kits for '99 - '02 F-body are made specifically for those cars and need some minor modification to become plug and play into a 3rd gen. The following instructions explain how to make those modifications. These modifications will void your warranty, but it is a cleaner install and will appear to be made for your car.
Note: If you don't want to go through the hassle of finding all the parts for this job then PM me and I can set you up with a harness.
You will not need the stock 4th gen wiring harness. Just toss it to the side because the Hotwire kit has the same connections to fuel tank only better. Although be aware that Hotwire kits are different than in the past and now come with the higher current GT 280 connector. You will need an adapter harness to bridge between that and the stock 4th gen bulkhead connector if you wish to keep the stock bulkhead.
All the wires you will be modifying are 18 AWG wire size. Part numbers of connector components you will need are,
These instructions will get you "Option 1" in the wiring schematics at bottom of this post. "Option 2" is identical except it lays an extra wire for fuel sender ground to the C313 connector.
Step 1: Begin tear-down by removing the square body connector that is intended to interface with stock 4th gen wiring harness. Discard the connector, you will not use it again. De-pin the small wires at fuel pump connector and discard the short 4-inch pigtails.
Step 2: Cut away the terminals from the small Black and Gray wires. These wires will be re-fitted later with different kind of terminals. Pull the Gray wire out of the loom back to the relay. This is the end of the tear-down.
Step 3: Now the reconstruction begins. Turn your attention back to the fuel pump connector. You should have 3 wires remaining in the bundle: The two large wires still tied into the fuel pump connector; and the small Black wire hanging free. Slip another 18 AWG wire into the harness (Purple is most desirable). Finish off the wires with GT 280 terminals and wire seals and fit the Black wire into Pin 1, and the Purple wire into Pin 3 of the Fuel Pump connector. Purple will serve as Fuel Sender signal, and Black will serve as Fuel Sender ground.
Step 4: Run the new Purple wire through the harness past the Relay. Take the Gray wire you fished out of the harness earlier and run it in a bundle with the purple wire to the C313 body connector behind the rear seat. Finish off the wires with Weather-Pack male terminals and seals and fit the Purple wire into Pin B, and the Gray wire into Pin C of the C313 connector.
Step 5: Plug the hole located at Pin A with a dummy wire and store the excess out of sight inside the wire loom. If you choose to do "Option 2" wiring schematic with Fuel Sender ground going to C313 connector, then fit that wire into Pin A. All you've got to do now is tidy things up and you're done!
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
I just pulled my binder with coffee stained notes from mid-2000s and you have just detailed almost the exact same process and configuration I did to my car. My saved notes have that ACDelco 25319676 as a Grand Prix p/n. My only real difference was for the fuel pump ground to body method. I set a rivnut an inch or two next to the passthru and secured a ground lug with a #10 UNC screw and star washers.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
QwkTrip - I have a thread about not being able to add gas to my 4th gen tank. A couple members replied with some items to check. You replied about the vent valve possibly being closed and maybe it can be opened by hooking up a battery to it. Another member replied stating the roll over vent might be closed. I’m planning to look into my issue this Friday to try and fix it. I’ll report the solution in my thread. Just thought some info on possible venting issues might be helpful to mention here since this thread is very informative and will hopefully be made into a sticky.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
I need to have a Racetronix Hotwire kit in order to take pictures to make instructions for this thread. Does anybody want to buy a new F99 kit (RFPK-001) and send it to me and I'll prep it for you and send it back?
Update: Ah, never mind, I bought a harness. I'll just sell it when I'm done.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Note: GM/ Packard Electric created the Pack-Con I/ Pack-Con II/ Pack-Con III/ Pack-Con HD Series (30A/ 40A)...
at the time for the newly created Blade Fuses (ATO/ ATC) that would replace the Glass Cylinder Fuses previously implemented.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
The Male Terminal for this Connection Series was an afterthought...
Male Metri-Pack 280 Terminals replaced them in some situations, like the C207 and C208 Connections.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
I haven't covered that yet in this thread. How much of a hurry are you in? I have a harness coming that I'm going to modify and take pictures to finish that part of the write up.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Originally Posted by QwkTrip
I haven't covered that yet in this thread. How much of a hurry are you in? I have a harness coming that I'm going to modify and take pictures to finish that part of the write up.
Not in a rush. My care hasn't had an access cut yet so I need to figure it out before I put the axle in. I still have to pull the old engine and trans so I have lots to do.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
@Leon82 , I still don't have all the parts needed to do a complete rework of the Racetronix harness. I posted up schematics so you can see how the wires change. It may be a little while though before I update with detailed instructions.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Originally Posted by QwkTrip
@Leon82 , I still don't have all the parts needed to do a complete rework of the Racetronix harness. I posted up schematics so you can see how the wires change. It may be a little while though before I update with detailed instructions.
Thanks,
I will look at them.
What fitting do you use for the fuel sender to go to an an line? The sender has a retaining clip on it.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Originally Posted by Leon82
What fitting do you use for the fuel sender to go to an an line? The sender has a retaining clip on it.
Russell 611253644123 if you're using -6 hose. It's a little shorter in length to give the hose enough room to make the turn away to the side of the tank.
For Harness/ Connector Assemblies that do not incorporate an Oxygen-Sensor/ or require additional "Strain-Relief"...
I highly recommend replacing the Delphi TPA #12160826, with Delphi TPA #12176368 instead.
See Image below:
Last edited by vorteciroc; 08-27-2022 at 05:57 AM.
Couldn't have done much of this without your expert help in the LS electrical connectors part numbers thread. That's really the key material needed to enable anyone to do all this stuff.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
@vorteciroc , got any suggestions what to use for splicing wires for harness build with Post #4 ?
That splice of 10 AWG wire with 2 x 14 AWG wires is a bigger job than what AMPLIVAR crimps were made for. I found the TE Connectivity catalog for wire to wire splices but so many choices.... so much to learn....
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Originally Posted by QwkTrip
@vorteciroc , got any suggestions what to use for splicing wires for harness build with Post #4 ?
That splice of 10 AWG wire with 2 x 14 AWG wires is a bigger job than what AMPLIVAR crimps were made for. I found the TE Connectivity catalog for wire to wire splices but so many choices.... so much to learn....
For what you described... this is what I would use:
Often Racing rules/ tech inspection tells us not to use the outside Shrink tube (obviously you can for your own car)...
they want Raychem SCL instead.
Product Hyperlink below from the Retailer that I would recommend for you: Hyperlink
Last edited by vorteciroc; 01-04-2023 at 09:46 PM.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Thanks. I was looking at that Mini-Seal product lineup too but it only goes to 12 AWG wire size. I'm guessing you don't bother with 10 AWG to feed a 340 L/hr pump? At 20 foot length, there is only 0.2V loss difference between 10 and 12 AWG @ 20 Amps.
I saw the SolderSleeve lineup and it goes bigger but I'm skeptical whether solder is a good idea for this kind of application.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
If I find a 12 AWG or 10 AWG Wire that does not fit (warning the Product line I posted above runs Smaller than most Butt-Splices from other Brands)...
Grab any Brand heat-shrink Butt Splice and remove (Cut and peel off) the Yellow outer layer:
The Perma-Seal Product line is what I have the most experience with.
Sometimes the heat shrink tube that came with the TE/ Raychem Butt Splice will fit over the Butt Splice that you removed the outside layer from.
I actually use those on Motorsports and MilSpec Harnesses that I do NOT want anyone taking apart.
The Center Locking Tang of that CPA is actually much shorter than the other Versions of the GT Series CPA Locks.
Shown in Image below:
The other Versions have a longer Center Locking Tang, so that the CPA Lock can be slid back and forth to separate the Connector halves...
and NOT have to take the CPA Lock off of the Female Connector half.
The #12191398 Purple CPA Lock can NOT slide back and forth (it can ONLY be removed completely... making it very unpopular compared to the other Versions).
I cut the Tether off of the Purple CPA Lock, and use it on Motorsports and MilSpec Connections.
(Almost like a permanent CPA Lock).
Last edited by vorteciroc; 09-01-2022 at 01:17 AM.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
It came with the Racetronix harness. They don't list it individually on their website but they'll sell you almost anything if you call. You'll have to talk to the owner though, don't work with the help staff. Honestly, a lot of the connector kits they sell are better price than Mouser, it's the shipping cost that'll get ya.
EFI Connection has it on their website but I don't know if they actually have inventory. Maybe worth a phone call too.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Originally Posted by QwkTrip
It came with the Racetronix harness. They don't list it individually on their website but they'll sell you almost anything if you call. You'll have to talk to the owner though, don't work with the help staff. Honestly, a lot of the connector kits they sell are better price than Mouser, it's the shipping cost that'll get ya.
EFI Connection has it on their website but I don't know if they actually have inventory. Maybe worth a phone call too.
Mouser is far from having the best Retail Pricing...
But they will sell One of any Component (Most Businesses do NOT, and will require that you purchase a large quantity of each Component).
Also they usually have great Stock/ Inventory/ Selection.
I do not usually buy from Mouser, unless I need One of something (or a small quantity of something).
Thanks, I will give Racetronix a call (they are only in Canada, I believe).
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Really appreciate the time investment and quality of this writeup. It was an enjoyable and educational read and I'm not even doing a tank swap right now.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Thanks for the kind words.
I'm kind of struggling to make an example of the harness for post #4. Still trying to figure out part number for grounding ring terminal. I found a Delphi TAXI for open barrel ring terminals but it doesn't go big enough wire size. I'm guessing other pages of that TAXI have the info I need but I can't get to it.
That's a lot of wire that has to be laid in that terminal, and it's getting hairy on the edge of violating guidelines for too much difference in wire sizes with a splice. Thinking maybe grounds have to be spliced further back in the harness and then terminate with single 10 AWG wire at ring terminal. Honestly thinking 12 AWG would be enough and that would solve some of my issues.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Originally Posted by vorteciroc
What size hole, and Wire/ Cable Gauge would you like?
In my case I have an M10 ground boss on the body. This is for grounds, 10 AWG pump + 18 AWG fuel sender.
Problem is the splicing guidelines I'm reading in the TE Connectivity tech documents recommends no more than 2 wire sizes different, so smallest would be 14 AWG spliced with 10 AWG. That's getting to be a pretty thick stack of wires for the tools I have. Anything larger than CMA equivalent for 10 AWG becomes a problem for me.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
I think I can deal with an 8 AWG closed barrel terminal but it's on the small side of what the tool can do and I never tried. I have a Tool Aid 18840, https://toolaid.com/product/18840
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
What I normally recommend for a NonMotorsports grade DIY solution is:
Strip/ prep the 10AWG Wire Conductors for the 8AWG Ring Terminal...
Strip a good 3" or so of the 18AWG Wire Conductors, and wrap them diagonally around the 10AWG Wire Conductors.
If not sufficient, a Copper Wire Ferrule can also be used in addition between the Wire Conductors and the Ring Terminal:
Sorry, I forgot to say...
Do not use a Wire Ferrule Crimper to crimp the Ferrule on to the Conductors.
Just Crimp the Terminal on to everything together.
Last edited by vorteciroc; 09-02-2022 at 03:11 PM.
Re: How to wire a 4th gen F-body fuel tank into a 3rd gen F-body
Originally Posted by Leon82
I measured the bucket fittings and they are 3/8 so I'm going to get the 611203
Sorry, my apologies. Somehow I carried that error through all my build documentation for many years and 2 different fuel systems. Not sure how I did that.
I do use 611203 on the hose drop from tank to my hard lines. I had a different part number of shorter length at the fuel tank bulkhead to get the hose to route nicely. Now I don't know what is that part number if my old documentation is wrong but looks like it was a non-swivel, maybe 644123 (I do have that p/n on a purchase receipt in my notebook).
07-30-2022, 08:10 PM
