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Old 01-30-2018, 09:32 AM   #14
hatzie
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Location: Wentworth, NH
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Re: 1973-1991 Dual fuel tank systems theory of operation

Quote:
Originally Posted by Popeye75356 View Post
Hatzie,
Thank you for the diagrams and info as I've swapped a 5.3 into my 84' SWB and I've purchased the FiTech Ultimate LS management system. I purchased the 87' baffled tanks along with 87' sending units and Walbro 255 pumps all already installed. My original harness obviously lacks power for the pumps as it ran off of a mechanical. I visited Painless today and one of their engineers drew a diagram for wiring up to the OEM switch as long as the FiTech system supplies the 12v power. My question is simple, is there a vendor that I can source an 87' harness so that I can "plug and play" the wires on the 87' sending units thereby powering my in-tank pumps and sending units when switching tanks or will I be relegated to fabricating my own harness???? Any help would be greatly appreciated. FYI I'm new to all of this ! Father passed away and I felt compelled to attempt a frame off on the only "NEW" truck he ever owned...........

Thanks in advance!
Popeye
You'll probably have to fab your own harness.

It's not as bad as it sounds. Lay the original out on a sheet of plywood and place nails at the bends and end points so you can lay out the new wires to match. Leave around 4-5" extra at the termination points and put wire ties at the breakouts to keep the wires organized til you wrap them with split poly or wire harness wrapping tape (NOT Electrical tape).

The factory connector part numbers are in the 88-91 schematics. Mouser Electronics and NAPA sell Weatherpak, Pak Con, and Delphi Packard 56 connectors and terminals.

The Pak Con ignition power connector for the system is obsolete. The Pak Con terminals are not. You can probably carefully liberate one off your factory motorized valve NL2 harness.

You will need to liberate the obsolete Packard 56 switch connector from your 81-91 factory motorized valve harness along with the firewall grommet and wire boot.

If your truck was not equipped with the NL2 dual tanks a 1/2" round hole, for a toggle switch, is much easier to drill than a rectangular hole for a GM rocker switch... you just use a 20A Polarity Reversing toggle switch and a Packard 56 keyed toggle switch plug 12052978 connector.
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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; 01-30-2018 at 09:59 AM.
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