Fuel tank and Guage questions

[Autonutz]

Hey guys I'm installing a second tank that I had and hooking up the tank switch and Guage.
Wondering if someone knows what the three lines are coming out the top of this tank? I have two that go to the valve but not sure of the order and why there is an extra....
Does anyone have a pic of the rear of their fuel gauge? I think mine may be missing a few items haha
Also wondering the location of the fuel gauge sender, is it with the valve switcher?

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[bd]

The sending unit is in the fuel tank - it has the pink (gauge) and purple (ground) wires connected to it in the image you posted.  The three tank lines are:  3/8" = fuel supply to pump, 5/16" = tank vent from vapor canister, 1/4" = fuel return from pump.  Since you have a tank selector valve, the 3/8" and 1/4" lines will plumb through the valve.  The 5/16" line will tee with the vent line from the opposite side tank and plumb to the vapor canister located left of the radiator.

Why do you think something is missing from the fuel gauge?

[Autonutz]

That makes a lot more sense, thanks again!

There is a black wire on the rear top of the fuel gauge, I'm  assuming that's the ground.
The rear bottom appears to be some circuit board material and has nothing attached or anything to attach too.
I was hoping to not pull the Guage cluster but it looks like it's starting to go that way!

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[bd]

Sounds like a work-around hack for a burned or faulty circuit board.

[Autonutz]

Ugh oh well, I'll pull it and see what find

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[Autonutz]

Just discovered that there is no evap cannister in my truck...

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[enaberif]

That is because most evap canisters after 40 years are useless and people remove them.

[bd]

AutoZone VC105 or similar

If the 5/16" pipe is still there, you can either install a new canister, a filter in lieu of the canister, or cap the line and use a vented gas cap.  But, one way or another, the fuel tank has to be vented.

[Captkaos]

Could your "ground" wire on the cluster be the fiber optic cable that runs to your ashtray.  There are no wiring coming off the cluster unless you have a clock or tach...

[Autonutz]

Turns out the tank I'm putting on (from an 81 k15 i sold) is smaller and the holes dont appear to line up, guess ill tackle it in the light when its not raining and get a better look!
I figure worse case scenario i have to drill a new set on one side making sure everything clears ok.

The other crazy idea i had was to get ahold of a suburban or blazer rear gas tank (25 gallons) in addition to the two other tanks, changing the tank splitter valve to a 3 way, piping it in and wiring it. This would eliminate the want/need for a slip tank under my toolbox as the full capacity would be 61 gallons...Slip tank might be cheaper in the end however!