The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 1973-1991 Dual fuel tank systems theory of operation

**hatzie** · 09-28-2019, 10:17 AM

I assume the wiring from the fuel pump relay to the Metripak disconnect on the NL2 wiring harness is OK.

If you have the whole NL2 harness it's not difficult to build a brand new one using the old harness as a layout guide. If you cut it in a couple places or it's broken in a few places just duct tape it together. You aren't trying to make it work again you're in need of a layout and wire length guide. Even if it's chewed up pretty badly it'll show where the wires need to be terminated and how long you need to make em.

I usually lay one of these small harnesses on a piece of plywood and drive in finish nails after the terminations and next to any breakout points.

The NL2 sub harness is actually in two sections.

The Weatherpak and Metripak 480 firewall disconnects to the switch and ground inside the cab.
Two position Weatherpak disconnect at the firewall to the Weatherpak valve plug, and the Weatherpaks at the senders.
[**]There's a single wire from the B terminal on the six position Weatherpak at the valve to a disconnect in the fuel gauge wire on the RH frame rail. Some of the later TBI trucks used a Weatherpak at this position. If yours is a molded rubber connector and this wire is chewed up I'd replace it with a single position Weatherpak and new wire.

You can buy the 2 position Weatherpak shells, Metripak 480 shells, all three terminal families (Weatherpak, Metripak 480, & Packard 56), and the Metripak/Weatherpak wire seals from Mouser Electronics.
The connector shells inside the cab are obsolete but the terminals are easy to source.

Download the 1989 wiring diagrams and print off page 34 (PDF page 42) on 11x17 paper. The connector shell part numbers are on the diagram along with the wire gauges and colors. I'd use 14ga SXL jacketed wire. You can get project assortments in 25' lengths from the Wirebarn.
The original harness was wrapped in harness wrap. This is not electrical tape it's a special friction activated tape. I'd use Split poly loom with Tesa harness tape at the joints and maybe wrap the split poly every 6" or so with two wraps of Electrical tape to keep the split closed.
https://www.amazon.com/Tesa-Wire-Loo.../dp/B00EH6IZ6Y

There are two splices in this harness, near the six position Weatherpak on the valve, for the fuel pump power feeds. I'd solder these joints and slip adhesive lined "marine" heatshrink over the connections.

Delphi 12085270 & 12085271 ratcheting terminal crimp tools are very versatile tools. They will do every original terminal in the square-body trucks from Packard and Pak Con to Metripak and Weatherpak. They're around $100 each but these are the most used crimp tools in my wiring box outside of my Daniels AF8 & AFM8.
There are some non ratcheting crimpers that are almost as versatile but they're unpleasant to use.
I'd buy the Delphi tools and sell em when you're finished... if you decide you don't want to keep em.

Gmachinz Harnessworx makes custom and factory type harnesses. I've never done business with him so I don't know what your experience will be.

09-28-2019, 10:17 AM	#49
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,915	Re: 1973-1991 Dual fuel tank systems theory of operation I assume the wiring from the fuel pump relay to the Metripak disconnect on the NL2 wiring harness is OK. If you have the whole NL2 harness it's not difficult to build a brand new one using the old harness as a layout guide. If you cut it in a couple places or it's broken in a few places just duct tape it together. You aren't trying to make it work again you're in need of a layout and wire length guide. Even if it's chewed up pretty badly it'll show where the wires need to be terminated and how long you need to make em. I usually lay one of these small harnesses on a piece of plywood and drive in finish nails after the terminations and next to any breakout points. The NL2 sub harness is actually in two sections. The Weatherpak and Metripak 480 firewall disconnects to the switch and ground inside the cab. Two position Weatherpak disconnect at the firewall to the Weatherpak valve plug, and the Weatherpaks at the senders. []There's a single wire from the B terminal on the six position Weatherpak at the valve to a disconnect in the fuel gauge wire on the RH frame rail. Some of the later TBI trucks used a Weatherpak at this position. If yours is a molded rubber connector and this wire is chewed up I'd replace it with a single position Weatherpak and new wire. You can buy the 2 position Weatherpak shells, Metripak 480 shells, all three terminal families (Weatherpak, Metripak 480, & Packard 56), and the Metripak/Weatherpak wire seals from Mouser Electronics. The connector shells inside the cab are obsolete but the terminals are easy to source. Download the 1989 wiring diagrams and print off page 34 (PDF page 42) on 11x17 paper. The connector shell part numbers are on the diagram along with the wire gauges and colors. I'd use 14ga SXL jacketed wire. You can get project assortments in 25' lengths from the Wirebarn. The original harness was wrapped in harness wrap. This is not electrical tape it's a special friction activated tape. I'd use Split poly loom with Tesa harness tape at the joints and maybe wrap the split poly every 6" or so with two wraps of Electrical tape to keep the split closed. https://www.amazon.com/Tesa-Wire-Loo.../dp/B00EH6IZ6Y There are two splices in this harness, near the six position Weatherpak on the valve, for the fuel pump power feeds. I'd solder these joints and slip adhesive lined "marine" heatshrink over the connections. Delphi 12085270 & 12085271 ratcheting terminal crimp tools are very versatile tools. They will do every original terminal in the square-body trucks from Packard and Pak Con to Metripak and Weatherpak. They're around $100 each but these are the most used crimp tools in my wiring box outside of my Daniels AF8 & AFM8. There are some non ratcheting crimpers that are almost as versatile but they're unpleasant to use. I'd buy the Delphi tools and sell em when you're finished... if you decide you don't want to keep em. Gmachinz Harnessworx makes custom and factory type harnesses. I've never done business with him so I don't know what your experience will be. __________________ 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... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF** 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; 09-28-2019 at 10:29 AM.