Gas tank sending unit wire

[Trailering Special]

Can anybody help me with a gas tank sending unit problem. I have a 78 scottsdale with dual tanks. The passenger side sending unit went out some time back and i am just now getting around to fixing it. As i dropped the tank and unhooking the hoses and wires i noticed the sending unit wire was totally gone except for the little connecter on top of the sending unit with a very small piece of wire coming out of it. I cannot find the original wire connecting to the sending unit on top of the tank to the truck harness.

[gmachinz]

If it helps, I build reproduction dual tank harnesses and I stock NEW OEM Delco/Polack switching valves also. The RH sending unit wire comes directly off the switching valve connector.....are those wires present?

[Trailering Special]

Yes the selector valve on the passenger side which is mounted on the frame still has the wire connected to it and it does switch the tanks. The fuel tank sending unit wire on top of the passenger tank has the little boot connector on the sending unit but the wire broke of right at the little connector that on the sending unit. I cant find under the truck where it comes from.

[hatzie]

Originally Posted by gmachinz

If it helps, I build reproduction dual tank harnesses and I stock NEW OEM Delco/Polack switching valves also. The RH sending unit wire comes directly off the switching valve connector.....are those wires present?

What you're describing is the 1981 and newer motorized valve system. On the 1981 and later systems you are correct.

However...

1978, if it's original, has a single wire solenoid valve. The dash switch controls the gauge so both sender wires go from the tanks to the dual tank firewall connection and then directly to the switch.

The Pollack 3 port solenoid valve is obsolete but Standard Motor Products still makes them. The 6 port Solenoid valve is no longer produced by Standard Motor Products, Pollack, or anyone else I'm aware of. If your Solenoid valve still works the gauge should be fairly easy to fix.

The 1978 system should have four wires exiting the firewall in a round molded connector between the transmission tunnel and the brake booster. The wire colors are TAN, LIGHT GREEN, TAN/WHITE, and LIGHT BLUE.
If I'm reading the schematic properly the RH sender should be the TAN/WHITE wire and the LH sender should be the LIGHT BLUE wire.

Follow the RH senders' TAN/WHITE wire from the firewall connector toward the tank and determine if it's damaged.

The tanks should have a grounding wire that the gauge will not work without. It'll be a short black or purple wire that's plugged onto a 1/4" male tang on or near the sender locking ring and a ring terminal on the frame.

If the sender wire is cut off or badly damaged ask gmachinz if Harnessworx can reproduce the molded pin connector for the sender with a long enough SXL pigtail in the color you need.

If the solenoid valve isn't working, and it's a 6 port valve, post again and gmachinz can set you up with a decent complete retrofit harness and the same Genuine Pollack Motorized 6 port valve that GM used... If you go this route I would recommend using the AC DELCO D7089C 87-91 RV series TBI dash switch on all 1981 and later motorized valve systems. They are more robust and completely interchangeable with the momentary AC Delco D7003 switch GM used on the 1981-1986 trucks. They're easy to tell apart the switch you do not want has "DEPRESS FULLY" at the bottom of the bezel...

[Trailering Special]

yes it has one single wire on the solenoid sending unit. I did not know if the sending unit connection on top of the tank was hooked up or if some previous owner cut it off. so you are saying that the passenger tank reading comes from the tank solenoid valove under the truck that only has one wire on it.

[hatzie]

Originally Posted by Trailering Special

yes it has one single wire on the solenoid sending unit. I did not know if the sending unit connection on top of the tank was hooked up or if some previous owner cut it off.

so you are saying that the passenger tank reading comes from the tank solenoid valove under the truck that only has one wire on it.

Only after 1981. I get carried away and explained too much. Between 1973 & 1991 there are two different dual tank systems. The dash switch controls the senders till 1980. The valve controls the senders from 1981-1991.

Easier to post the 1978 Option NL2 snippet from the schematics... Solenoid is the valve. Fuel meters are the senders. The control switch is a good old fashioned DPDT rocker switch with one terminal removed as a key.
You can download the whole wiring book from the manuals link in my signature.

[Trailering Special]

I am not a real good electrical guy. The passenger sender unit on top of the tank has the plastic connecter on it with the wire cut off. With that cut off how does the gauge inside the truck get a tank reading on that side? The gas gauge does work when i flip the gas selector switch to the drivers gas tank on the dash. The gas tank selector solenoid under the truck has only one wire coming out of it with no pigtail or evidence of tampering. Thanks for everyones patience and input.

[hatzie]

Originally Posted by Trailering Special

I am not a real good electrical guy.
These are not difficult. The above schematic is just the dual tank circuit without any other clutter.

The passenger sender unit on top of the tank has the plastic connector on it with the wire cut off.
That's why the gauge doesn't work on that side. I assume this is a TAN wire with a WHITE stripe.
How many inches of wire are left on the connector?
With that cut off how does the gauge inside the truck get a tank reading on that side?
The gauge can not work till you hook that wire back up to the gauge half of the tank rocker switch in the dash. See below...

The gas gauge does work when i flip the gas selector switch to the drivers gas tank on the dash.

The gauge is OK and the BLUE wire from the LH sender to the switch and the TAN wire out to the gauge are all OK.
The gas tank selector solenoid under the truck has only one wire coming out of it with no pigtail or evidence of tampering.
RIGHT... It should be a LIGHT GREEN wire according to the above schematic. This wire is only HOT when the switch is set to AUX. The Selector valve does nothing with the sender wires on Pre-1981 dual tank systems.

Thanks for everyones patience and input.

This is the sender or FUEL METER female pin connector that snaps over the male pin and plastic insulator. I assume this is plugged in and has a cut TAN/WHITE or LIGHT BLUE (probably TAN) wire dangling from it on your truck.

This graphic shows two and three hose senders with the ground connector on the sender CIRCLED IN RED and the unhooked male sender pin connector CIRCLED IN GREEN...
The ground wire is a short, maybe 12inch, Purple or Black wire that runs to the frame.

[Trailering Special]

Yes that is it. The unit has a two outlet. I am trying to find out where the wire thats coming off the sending unit connects to . Its cut? SO THE MALE CONNECTOR DOES NOT HOOK TO ANYTHING? IT DOES HAVE THE GROUND WIRE IN PLACE.

[hatzie]

Post a picture of the sender with the cut off wire.

[Trailering Special]

Okay guys here is a picture of the passenger tank.

[hatzie]

Your ground wire is OK... The ring terminal needs to bolt to the frame.
Unfortunately the sender connection is cut way too short to repair using that connector. It's the connector in my post above that has some wire on it... The cut off end of that wire should be near the end of the harness wrap with the green solenoid wire. It runs all the way up to the firewall dual tank disconnect. Looks like it's TAN which matches the schematic.

I bought a good un-molested 73-80 NL2 dual tank harness for my 1976 before I discovered I couldn't source the dead 6 port valve. I have it in a box on the shelf.
This is what the 73-80 sub-harness should look like.

Inside the cab. Left to Right; Rocker Switch, Rocker switch plug, Power connector (PINK wire blue plug), Round molded firewall passthrough connector.


From firewall to valve and tanks.
Left to Right; Round molded firewall passthrough connector Engine bay side, LH sender BLUE female pin, RH sender TAN female pin, gauge wire male pin WHITE, Solenoid valve stud sleeve connector GREEN.


gmachinz probably has or can make the tank connector with enough of a tail to re-attach it to the rest of the tank harness.

[Trailering Special]

I would like to thank senior member hatzie for his never ending help with my tank sending unit wiring issue. I will need to make a trip to the junk yard now to try to find my harness. Thanks for the help.

[hatzie]

Honestly I'd repair what you have. I doubt it's more complex than soldering a pigtail with the sender connector to the cut off end of the RH tank wire. You should be able to use any 1970's GM sender wire.
http://www.americanautowire.com/shop...FVFZhgodKEAJJg should work OK as a repair pigtail.

It took me months to find that unmolested harness. Most of them are like yours.

[Trailering Special]

Thanks, i will try that instead, i need to get restarted on it . Lol. I have been busy with work. I will update my progress. I did notice that as the harness one wire went to the solenoid the other pluggged into a wire running along the frame rail going toward front of the truck. The one that did not look normal was the last wire coming out of the harness was grounded to the frame. It was not a factory connector, it had been cut and a ilet type was crimped on the end and screwed it to the frame as a ground.

[hatzie]

Originally Posted by Trailering Special

Thanks, i will try that instead, i need to get restarted on it . Lol. I have been busy with work. I will update my progress.
I did notice that as the harness one wire went to the solenoid the other pluggged into a wire running along the frame rail going toward front of the truck.

The one that did not look normal was the last wire coming out of the harness was grounded to the frame. It was not a factory connector, it had been cut and a eyelet type was crimped on the end and screwed it to the frame as a ground.
Bet that's a TAN wire with a WHITE stripe or just plain TAN in that oddball ring terminal. Bet the gauge goes to E when you select the RH tank too.

If the end of the dual tank harness doesn't tin with electronics solder and paste flux... I'd connect them with a one pin Weatherpack connector on the repair pigtail and the cut tank harness wire.

If the solenoid valve isn't working you are not SOL. You have 2 port sender... That's fuel feed and vapor with no return. Meaning you can use the FV1 three port valve that's still being manufactured by Standard Motor Products.

[Shady Rascal]

For what it's worth, I went through something similar recently on my 74 truck. I needed the pigtail end that plugs onto the sending unit. I wound up getting it from Rockauto for 2.59 cents. It plugged on and worked perfectly and came with plenty long wire to splice in to.

picture taken just seconds before I messed up the connector and had to order a new one.



AC Delco PT197

https://www.rockauto.com/en/moreinfo...k=251559&jsn=1

[Trailering Special]

After i fix the connector i need to find where in the hareness it ties into under the truck.

[Trailering Special]

I have the gas tank sending unit connector repaired finally. I see the harness that has three wires coming out of it one going to the solenoid and the other is running a long the frame rail towards the front of the truck and the other wire is grounded to the truck frame which does not look right. I can not find where the sending unit wire on the passenger tank connects to the harness under the truck.