NH WTB Complete Dual tank harness from all three square generations.

[hatzie]

I need dual tank sub harnesses for two generations of the squares.
They need to be complete enough that they have all the factory connectors (including the molds) and all of the original wires in place.
I need to determine the length of wires needed to replicate them. If the wires have damaged insulation from rubbing etc but there are no cuts or breaks it will meet my needs.


All 81-86 C/K or 87-91 R/V Diesel Motorized valve all three sections.

1. Switch to firewall including fuse panel power and ground wires.
2. Firewall disconnect to valve, frame disconnect, and senders.
3. Frame disconnect to bulkhead plug wire.

87-91 R/V TBI Motorized valve all three sections.

1. Switch to firewall including fuse panel power and ground wires.
2. Firewall disconnect to valve, frame disconnect, and fuel pump power/senders.
3. Frame disconnect to bulkhead plug wire.

[SilverMiner]

PM sent

[GonicGM]

There were at least two styles for 81-86 (87-88 carbureted) The diesel is different than gas. If I read your post correctly, #3 is actually part of the engine harness. I may have some of the harnesses you are looking for.

[hatzie]

There are only three RPO NL2 sub harnesses used from 73-91.

#1 73-80 use a single wire solenoid valve and the dash switch changes the sender connection.
#2 & 3 are motorized valve systems. The valve controls the sender connection.

#2
All 81-86 are the same sub-harness regardless of fuel used.
All 87-91 diesel and 81-86 are the same sub-harness.

#3
Look at the 1987 GMC Factory wiring diagrams in my signature. PDF pages 203 (TBI #3) & 204 (Diesel #2). The 88-91 diagrams are easy enough to dig through to find the NL2 option wiring. I've already looked at them. If you want to see... download em and find the NL2 pages yourself.

87-91 TBI integrates the fuel pump into the dual tank harness by tapping into the reversible polarity wires on the valve.

87-91 TBI isn't integrated into the engine harness. The switch is wired directly to a fuse panel "A" position that's powered only when the ignition is switched on. See PDF pages 164 & 165 of the 1987 GMC Factory wiring diagrams.

[hatzie]

I am still looking for the #2 & #3 NL2 sub-harnesses.

[GonicGM]

I have an 83 K2500 6.2 Diesel that has a different dual tank harness than the 83 K30 I have, gas engine. The diesel has water in fuel dash indicators and thus has two pin connectors to the fuel sending units, not one as the gas truck does.

1973 and perhaps 1974 had mechanical cable dual tank switching not electric, IIRC. Need to look in parts book.

I have a library of GM parts books, service manuals, unit repair manuals and wiring diagrams. I have several of these trucks and parts to build dozens more. There are countless errors in the GM printings. I have boxes of these dual tanks harnesses. if you don't believe me, come by. I can prove it. I'll show you all the different versions that in fact exist, regardless of the wiring diagrams and parts books. Yes, they are all GM.

[hatzie]

There are always low production number orphans.
I'm looking to build three harnesses to cover 95% not all the orphans.

WIF on the sender probably goes along with the 82 & 83 "diesel only" water drain valve in the rear spring hanger?

I know my 84 Civvy diesel used the sensor in the Stanadyne Model 80 filter not a sensor in the sender assembly. The Stanadyne Model 80 pot metal fuel filter base had WIF sensors that eventually leaked like a sieve. One of the main reasons I replaced my Model 80 POS with a 1998 manifold mount top loading FFM 6.5L fuel filter assembly on the CUCV.

1980 is an orphan as well. It has a timer relay between the fuse panel and the dash switch to keep the valve energized in the start position. The 73-79 harness will work on these trucks.

NL2 was available in 73 & 74. The 73 & 74 solenoid valve is different from the 75-80 valve but the 75-80 valve is the only replacement.

The early cable valve system is a different option noted in the wiring diagrams as Auxiliary Tank Switch or some such. It used a dash switch and very close to the same harness to control the fuel gauge (no solenoid power wires). I ran a 73 C60 on our farm with this setup and I could look at the fuel levels in both tanks without switching the valve. The C60 is long gone.

I scanned most all the service manuals I have... so my library is an open book.

[GonicGM]

Here are three 81-86 NL2 dual tank harness, #2 per your list? There are two different style bulkhead connectors, one with two pin and the others with three pin. On the three pin, only two of the positions are used. I'm rather certain that these are all from gas trucks. IIRC, the three pins utilized a dedicated feed through grommet and pins. There was no wiring related to the bulkhead feed through. It was a short boot grommet with pins both sides and harnesses with molded plugs meeting it on both sides.

Price is $30 each or $50/pr plus ship or pickup. Mention which ones you are interested in and I can provide details of flaws. I'll dig for others when I get a chance.

[gmachinz]

I already have mockups in testing for 73-80 and 81-87 dual tank harnesses replacements....are you wanting old harnesses or new? I don't stock the selector valves or switches but everything else I've sourced. Let me know-thanks!

[legendman]

I have some of the harness out of a 84 k20 and some from a 82 K30 both had 6.2s
Let me know.