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Old 04-03-2019, 08:37 PM   #1
focusedontheprize
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Fuel Tank Sending Unit Connector/Harness

Almost done with tidying up the harness in the truck. The truck was originally a TBI truck, but someone removed the motor and "modified" the harness to get it to work.

The last puzzle piece (at the moment) is the fuel tank sending unit connector. I need to replace the wire and realized the fuel tank sending unit connector is falling apart and is not salvageable.

This is what it looks like (below). I took some quick measurements and mine measures 0.420" ID and 0.560" OD. Has anyone swapped this prior and do they vary in size? I thought the one on my 1986 was larger.

Either way I did order it from RockAuto to see.
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"Dixie" - 1988 Chevrolet V30 CCDRW "3+3" | 7.4L 454 (L19) | TH400 | 8" lift and 37s" (will be going to a 4" lift and 35s")

"Lucille" - 1949 Chevrolet 3100 | 292 | T5 | 8.8" | 5" drop | The rebirth of Lucile.. (on hold)
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Old 04-04-2019, 04:49 AM   #2
Wgesnerjr
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Re: Fuel Tank Sending Unit Connector/Harness

I swapped an 87 (fuel injected) sending unit into my 85 (non fuel injected). the stock wire from my 85 fit right on the 87 sender with no problem.

UPDATE-UPDATE-UPDATE
Just went back and looked at pictures from my build and the stock 85 connector will not work on the 87 sender unit. the ohm reading is the same but the plug is totally different. sorry for the confusion.
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Last edited by Wgesnerjr; 04-06-2019 at 09:23 PM.
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Old 04-04-2019, 06:00 AM   #3
focusedontheprize
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Re: Fuel Tank Sending Unit Connector/Harness

Thanks Jay, that is good to know. The wire I had pulled out had been spliced in (they used a brown wire) so I could not determine if that was the original wire or not.

For now I will run the wire and have to wait to solder in the new connector.
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"Dixie" - 1988 Chevrolet V30 CCDRW "3+3" | 7.4L 454 (L19) | TH400 | 8" lift and 37s" (will be going to a 4" lift and 35s")

"Lucille" - 1949 Chevrolet 3100 | 292 | T5 | 8.8" | 5" drop | The rebirth of Lucile.. (on hold)
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Old 04-04-2019, 08:53 AM   #4
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Re: Fuel Tank Sending Unit Connector/Harness

Quote:
Originally Posted by Wgesnerjr View Post
I swapped an 87 (fuel injected) sending unit into my 85 (non fuel injected). the stock wire from my 85 fit right on the 87 sender with no problem.
The 87-91 TBI sender has a two position Weatherpak that connects to the fuel pump and the sender rheostat along with a Ring terminal for the frame ground. All three wires go through a grommet in the top of the sender.

87-91 diesel and 454 carburetor engines used the older 73-86 senders.

The 73-86 engine sender is a brass pin to mate with the molded rubber single pin connector shown in the first post. The frame ground wire on the carburetor and diesel senders is a separate piece that connects a 1/4" tang on the sender ring to a ring terminal on the frame.

If you need a new rubber pin connector just get a 70's A-Body (Chevelle, LeMans, Skylark) or F-Body sender pigtail from Classic or Year One or ...
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


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Old 04-04-2019, 09:59 AM   #5
focusedontheprize
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Re: Fuel Tank Sending Unit Connector/Harness

Quote:
Originally Posted by hatzie View Post
The 87-91 TBI sender has a two position Weatherpak that connects to the fuel pump and the sender rheostat along with a Ring terminal for the frame ground. All three wires go through a grommet in the top of the sender.

87-91 diesel and 454 carburetor engines used the older 73-86 senders.

The 73-86 engine sender is a brass pin to mate with the molded rubber single pin connector shown in the first post. The frame ground wire on the carburetor and diesel senders is a separate piece that connects a 1/4" tang on the sender ring to a ring terminal on the frame.

If you need a new rubber pin connector just get a 70's A-Body (Chevelle, LeMans, Skylark) or F-Body sender pigtail from Classic or Year One or ...
As always thank you Hatzie for this. Question for you:

I traced the wire from the sending unit to inside the engine compartment where they spliced it into a harness that had a two port Weatherpack that ran through the firewall and (facing the firewall, it would have been to the right of the throttle cable) into the cab. That harness (I believe black and a brown wire) was routed inside the dash and came to a plug that looks exactly like a dual tank switch that is on the dash. Again it was built of dark colors (brown, grey, black)

Is this the harness for the dual tank switch and since I no longer have a TBI (and have a dual tank switch harness already replaced in that spot), I would no longer need it?
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"Dixie" - 1988 Chevrolet V30 CCDRW "3+3" | 7.4L 454 (L19) | TH400 | 8" lift and 37s" (will be going to a 4" lift and 35s")

"Lucille" - 1949 Chevrolet 3100 | 292 | T5 | 8.8" | 5" drop | The rebirth of Lucile.. (on hold)
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Old 04-04-2019, 12:02 PM   #6
hatzie
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Re: Fuel Tank Sending Unit Connector/Harness

Quote:
Originally Posted by focusedontheprize View Post
As always thank you Hatzie for this. Question for you:

I traced the wire from the sending unit to inside the engine compartment where they spliced it into a harness that had a two port Weatherpack that ran through the firewall and (facing the firewall, it would have been to the right of the throttle cable) into the cab. That harness (I believe black and a brown wire) was routed inside the dash and came to a plug that looks exactly like a dual tank switch that is on the dash. Again it was built of dark colors (brown, grey, black)

Is this the harness for the dual tank switch and since I no longer have a TBI (and have a dual tank switch harness already replaced in that spot), I would no longer need it?
It sounds like that's the original NL2 dual tank harness. Those wires originally ran from the switch to the Pollack Valve Plug motor terminals D & E.

Your sender wires should run from the senders to the Pollack Motorized valve plug A & C terminals. The Pollack Valve B terminal should contain a wire that runs to a disconnect on the RH frame rail.

See post 2 in this thread for details on how the system on your truck originally worked.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061

Converting the senders from TBI to single wire on an NL2 dual tank truck is Extremely simple. As long as the orignal NL2 sub harness is in one piece... There's no need to pull new wiring into the truck and there's no need to butcher the existing sub harness so it's irreversible.
If the TBI senders are no longer serviceable you can liberate the wiring needed for the changeover from the senders.
  1. Unplug the two position Weatherpak sender plug from the NL2 harness in the truck. Leave the truck harness alone til you plug in your new sender pigtails.
  2. Cut the sender ground wire off at the top of the TBI sender and crimp a 1/4" female disconnect to the end of the wire for the carburetor sender tank ground.
  3. Cut the 2 wires routed to the 2 position Weatherpaks off the at the top of the TBI senders with at least 6" of wire.
  4. Purchase or otherwise source a molded GM fuel sender pin connector with at least 12" of wire.
  5. Connect the molded pin plug pigtail to the sender wire on the Weatherpak plug you liberated in step 3.
  6. Loop the end of the fuel pump wire over @ 1" and cover it with adhesive heatshrink to seal the end.
  7. Tape the fuel pump wire to the sender wire and cover the resulting sender pigtail with split poly loom.
  8. Plug the two position Weatherpak plugs into the truck harness and the tank.
  9. Plug the tank ground you made in step 1 onto the tank sender ring ground tang.

If the senders and fuel pumps are serviceable... don't chop em up. You can sell them or give em to someone that needs em.
You still need to make up the pigtails but it's not difficult.
Parts:
  • two 2 position Weatherpak tower shells,
  • two female Weatherpak terminals,
  • two Weatherpak cable seals,
  • two Weatherpak cavity seals,
  • several feet of 12ga SXL black wire,
  • several feet of expanding mesh wire sleeve,
  • molded pin sender connector pigtails,
  • two ring terminals,
  • two 1/4" female disconnect terminals.
  1. Slip some expanding mesh sleeve over the molded pin connector pigtail leaving @ 2" uncovered wire then strip and crimp the Weatherpak seals and terminals on the ends.
  2. Make up two black sender to frame ground wires that will reach... Strip and crimp the ring terminals on one end, slide some expanding mesh over the wire leaving @ 2" uncovered then strip and crimp on the Female disconnect terminal.
  3. Insert the cavity seal in the fuel pump power wire position of the Weatherpak shell. This safely terminates the connection without chopping it off the truck harness.
  4. Insert the Weatherpak terminal in the sender position of the Weatherpak shell.
  5. Plug the parts into the truck and test.

If you aren't comfortable crimping Weatherpak terminals and seals onto a wire you can buy Weatherpak repair pigtails and make them up just as you would've with cutoffs from the original senders.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old 04-06-2019, 03:37 PM   #7
focusedontheprize
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Re: Fuel Tank Sending Unit Connector/Harness

Thanks Hatzie. The harness was butchered beyond recovery, so I did end up pulling it out. It also was not connected to the actual rocker switch for the dual tanks.
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"Dixie" - 1988 Chevrolet V30 CCDRW "3+3" | 7.4L 454 (L19) | TH400 | 8" lift and 37s" (will be going to a 4" lift and 35s")

"Lucille" - 1949 Chevrolet 3100 | 292 | T5 | 8.8" | 5" drop | The rebirth of Lucile.. (on hold)
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Old 04-08-2019, 05:53 PM   #8
hatzie
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Re: Fuel Tank Sending Unit Connector/Harness

Quote:
Originally Posted by focusedontheprize
Hi Hatzie,

Since the TBI harness was butchered and I removed it, can I now run a single wire to the connector to power it from the fuse block?

I was trying to determine what circuit I could use that would still work on the fuel gauge.

Thank you again for the help.

From the sounds of things the previous owner made a big mess of the wiring...

The Fuel, Oil, and Temp gauge have Power, Ground, and Sender leads. The Senders provide a changing resistance to ground.

The 73-91 fuel sender is not powered by anything. It's a high wattage 0Ω-90Ω variable resistance between a ground on the frame of the vehicle and the sensor stud on the fuel gauge. 90Ω is FULL and 0Ω is Empty. If you don't want a fire don't put power on that wire.

The NL2 fuel sender wire from the valve is originally plugged into a pin connection, like the one in your original post, on the RH frame rail forward of the fuel valve. This wire is the stock single tank sender wire for trucks without the NL2 dual tank option so it has enough slack to reach the Passenger side tank sender. If the PO hadn't butchered the harness or time hadn't eaten the connector you could've unplugged this connection from the NL2 harness and plugged it directly onto the tank you are using.

Are you intending to wire up two tanks or just use one?
__________________
1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 04-09-2019 at 04:03 PM.
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Old 04-12-2019, 06:16 AM   #9
focusedontheprize
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Re: Fuel Tank Sending Unit Connector/Harness

Quote:
Originally Posted by hatzie View Post
From the sounds of things the previous owner made a big mess of the wiring...

The Fuel, Oil, and Temp gauge have Power, Ground, and Sender leads. The Senders provide a changing resistance to ground.

The 73-91 fuel sender is not powered by anything. It's a high wattage 0Ω-90Ω variable resistance between a ground on the frame of the vehicle and the sensor stud on the fuel gauge. 90Ω is FULL and 0Ω is Empty. If you don't want a fire don't put power on that wire.

The NL2 fuel sender wire from the valve is originally plugged into a pin connection, like the one in your original post, on the RH frame rail forward of the fuel valve. This wire is the stock single tank sender wire for trucks without the NL2 dual tank option so it has enough slack to reach the Passenger side tank sender. If the PO hadn't butchered the harness or time hadn't eaten the connector you could've unplugged this connection from the NL2 harness and plugged it directly onto the tank you are using.

Are you intending to wire up two tanks or just use one?
My intentions are to wire up both tanks.

After reading through the wiring diagrams, it looks like the LE8 setup for 1988 ran a single pink wire from Circuit 30 (30 .8 Pink) with the connector to the connector for the selector valve.

So with that in mind, shouldn't I be able to replicate this for my application?
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"Dixie" - 1988 Chevrolet V30 CCDRW "3+3" | 7.4L 454 (L19) | TH400 | 8" lift and 37s" (will be going to a 4" lift and 35s")

"Lucille" - 1949 Chevrolet 3100 | 292 | T5 | 8.8" | 5" drop | The rebirth of Lucile.. (on hold)
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Old 04-12-2019, 08:23 AM   #10
hatzie
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Re: Fuel Tank Sending Unit Connector/Harness

That's exactly what you want to replicate.

If you don't have the male and female molded pin terminal for the frame disconnect in the circuit 30 wire from the valve i'd just use a single terminal Weatherpak.
__________________
1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old 04-12-2019, 09:13 AM   #11
focusedontheprize
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Re: Fuel Tank Sending Unit Connector/Harness

Quote:
Originally Posted by hatzie View Post
That's exactly what you want to replicate.

If you don't have the male and female molded pin terminal for the frame disconnect in the circuit 30 wire from the valve i'd just use a single terminal Weatherpak.
Thanks Hatzie. The female molded pin terminal just arrived from RockAuto and I have the male molded pin terminal still connected in great shape so I will wire it up today.
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"Dixie" - 1988 Chevrolet V30 CCDRW "3+3" | 7.4L 454 (L19) | TH400 | 8" lift and 37s" (will be going to a 4" lift and 35s")

"Lucille" - 1949 Chevrolet 3100 | 292 | T5 | 8.8" | 5" drop | The rebirth of Lucile.. (on hold)
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