dual fuel tank operation

[camo36]

Hey everybody, just bought this truck, 75 4x4 with a 350....the driver's side fuel tank works fine, but the gas gauge doesnt...whatever...not too worried about it cuz i always carry gas when i wheel.  anyway...the passenger side doesnt work...can anybody explain the general operation of these dual tanks? 
Does each tank have its own fuel pump?
The switch in the cab is intact...but not in very good shape...i think with some general knowledge of how the system works i'll be able to figure everything else out on my own...or with more help from you guys.

any help is appreciated...

[Blazin]

Unless someone modified the truck it should have a mechanical fule pum on the motor. The switching valve is inside the frame rail unerneath about the seat area on the right hand side. Usually you can hear them work when you switch the dash switch. A new valve is approx $80 at Autozone, and a new dash switch is about $15 at Autozone.

[camo36]

alright, i'll take a look at the truck.

what kind of valve am i looking for at autozone?

[Blazin]

They should be able to look it up by aplication. I would check it out first before buying a new one. Could be a wiring problem?

[86swb]

If you get the right tank to work make sure you do a good job of cleaning it out. Most likely it has been that way for some time and it is always a good idea to drop the tank and have it cleaned out before putting fresh gas in.

[Hank Hill]

On a truck that old if your going to drop the tank you might as well replace it a long with the sending unit( to fix fuel gauge) and your rubber fuel lines. On my 81 everything was rotten and rusted. Your not going to do all this in a couple of hours either.
PS Plan on lifting your truck bed to do this.

[DnStClr]

camo36, what does your gauge do? Does it stay at zero or does the needle go past full?

[cjtimp]

Mine goes past full...was working good until I removed cluster to replace some bulbs in the back of cluster. Now goes WAY past full. When key is off it only goes to half.....I have rotten luck --fix bulbs now fuel gauge don't work right.....

[werewolfx13]

IIRC, going way past full is a problem in the cluster..

[Bitzer!]

or poss the sender wire going to ground thus completing the circuit?

[VileZambonie]

An open circuit will send the gauge past Full. A shorted circuit will read Empty

[velojym]

Years ago, while cleaning the instruments (oops... those markings come off way too easily), I also knocked
something outta line.
This was in my old '74 K10 with dual tanks. It didn't matter to me operationally, though, as I switched tanks
every time I got gas. Let one run low (or out), switch to the full one, and fill the empty one ASAP.

Doesn't really help with your issue, but it worked for me until I sold the truck. Still kinda kicking myself over that.

[choptop]

I have had over 15 of these trucks over the past years and have never replaced the fuel selector valve, however, the selector switch lasts 2-3 years normally in dusty enviroments and is where Id start first. Cheaper, easier, and probably needs it any way. As far as the gauge, I have been here many times, mostly when a bored friend is sitting next to you while you work on your ride, and plays with the gauges. It is a little un-orthodox, but I fueled up the truck and with a little finess, move the needle in the direction it needs to go. Turn off the ignition, move the needle a little past, and recycle the key. Since yours is showing half when the switch is off, move the needle to empty when the switch (ignition) is off, and try it. This has worked for me 9 times out of ten, Since if is half when off and way past full when on, I believe the needle is just out of since. And like velojym said, the markings on the gauge come off very easy. Wipe off with a dry soft cloth, but no cleaner at all.

[Hank Hill]

And like velojym said, the markings on the gauge come off very easy. Wipe off with a dry soft cloth, but no cleaner at all.

Compressed air also works great for cleaning off the gauges.