Fuel Tank Install

[rugbychevyguy]

I have an 84 K10 that has only an auxiliary tank in the back. I want to install 20gal saddle tanks, but have no tanks, filler necks, sending units, selector valve and i don't know exactly how the auxilary tank is wired up. Does anyone have a list of things that are needed or a good diagram of what the fuel delovery is supposed to look like with hard lines, selector valve, fuel gauge and sending units. Any help is appreciated.

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[VileZambonie]

Check the tech pages and the service manuals. Everything is in there

[zieg85]

Longbed or shortbed truck?

[hatzie]

I have an 84 K10 that has only an auxiliary tank in the back. I want to install 20gal saddle tanks, but have no tanks, filler necks, sending units, selector valve and i don't know exactly how the auxiliary tank is wired up. Does anyone have a list of things that are needed or a good diagram of what the fuel delivery is supposed to look like with hard lines, selector valve, fuel gauge and sending units. Any help is appreciated.

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20 gallon tanks will only fit a long bed.
You'll need;

• 1981-1991 Fuel tank doors with fill tubes and mounting hardware.  You'll also need SAE J30R6 filler hose and SAE J30R6 filler neck vapor hose.  Complete hoses and filler neck parts are available. Use Breezeliner clamps don't use regular worm clamps because they don't have an extended tang to protect the hose from the worm slots.
• Two 16 or 20 gallon tanks.  Short box trucks will only do 16gal tanks.  I highly recommend using 1987-1991 RV series baffled TBI tanks.  The 1981-86 CK series senders fit the TBI tanks just fine and a new baffled RV tank is the same price.
• All four 1973-1991 Fuel tank supports with straps.  There's a front and rear support on each tank and 16 & 20 gallon tanks use the same supports.  LH & RH supports are the same just rotated 180° keeping in mind there's front and rear support.  Squeak straps can be cut from 30# asphalt roofing felt or purchased. Complete supports are available.
• Senders seem to have some issues with bouncing gauge needles.  Aftermarket seem to be worse.  Get AC-Delco or Delphi if you can find them.  Some folks have reported bouncing fuel gauge needles while sitting still.  I recommend soldering a piece of copper braid from the float arm to nearby non-moving metal on the sender body.  This makes sure the sender rheostat wiper on the arm is always making contact with the grounded tank. 
• The supply and return plumbing runs from both tanks to the valve on the RH frame rail and then forward to the fuel pump. Vapor line runs from both tanks to a Tee near the valve and then forward to the charcoal can.  Hose routing is in the parts books and some of the service manuals.  Use SAE J30R9 hose with properly sized Constant Tension Band Clamps or German Fuel Injection Clamps.
   NOTE: Don't use worm clamps on the fuel lines they damage the hose and don't hold well.
• Find a wiring harness, Switch, and Valve.  The harness will likely need to be sourced used.  The big boys aren't making them.  I have delusions that I might but I'm nowhere near doing so.  There's an in cab section and under cab section.  Get the AC-Delco D7809 Switch that shows application for 1987-1991 only.  The OEM GM motorized valve was made by Pollack I've had less than stellar results with others. The Pollack datasheet shows wiring for three tanks...  http://products.pollakaftermarket.com/Asset/42-159%20IS_41-revdd.pdf

Manuals and parts books are linked below.
The 1984 wiring manual is in my bucket but not on the board.