Gas Tank Switching-gizmo

[Jim Molloy]

Have factory saddle tanks on my Grey Ghost(tm) stepside.Has the switch on the dash to change tanks.

First -gas gauge is always past the full mark doesn't move.

Second- tanks don't switch - ran the right side dry the left side
is full . Siponed a bunch out just to use it up.

Third- gizmo valve thing is on the right side frame rail by the
right side gas tank.Has four hoses going to it. Assuming this is
the tank switching device. Wire going to has power off and on
when using the dash switch.Can't feel anything move or vibrate
on the device when the dash switch is moved.

Now-I'm I right in saying this is the device that switches gas tanks ? Do I buy it at the dealer only ?

About the gas gauge-when the wire is grounded should the dash
gauge show full or empty ? How about if the wire is seperated from the sending unit what should the gas gauge show ?

To change the sending unit do the tanks have to come down off
the truck ? Looks like those hoses are cracked anyway.

Do all the fuel hoses from the tanks to the switched device enter
the top of the gas tank ?

Suggestions ,ideas and future winning lottery numbers appreciated ............

[Russell]

I've got an extra tank switch that isn't compatable with my truck, It has two hoses going in, and one coming out, no venting stuff which my truck needs...

If you figure you can use it - $10.00 cnd plus shipping

[Jim Molloy]

thanks,but mine has four hoses coming and going..must be
vent or return hoses..but just in case ...does it click when 12volts
is put to it.

need to get me a manual so I can see what the factory did..

maybe the vent hoses can be changed and go to vented caps.

anyone like a certain brand of manual better ? is it best to get
the factory book ?

[MSL]

Its called a fuel selector valve and to be honest with you i didnt replace mine from the dealer i got a borg warner one and it works awesome.

[74Pumpkin]

Russell

I might be intrested in the valve yo have. Do yo have a picture handy? It might fit the 74.

[Russell]

I'll snap a picture of it tommorow

[mike reeh]

jim what vehicle is this? what year, engine, etc

and you say there are a total of FOUR rubber lines connected to the valve?

mike

[79BIG10]

4 ports? I'm with MIke that it sounds strange. But who knows with GM. Here's some info that might help you diagnose your problem:
Does your gauge move when you switch the tanks? Have you been kicking or moving anything near your fuse block panel? Just a few questions to help diagnose.
Now here's a couple ideas:
On your interior valve switch replace it. To me it sounds like you have a bad switch. I got mine with cover for like $10 from the dealer. Don't use the Auto Zone stuff. The dealer is a couple bucks more but why waste on something that isn't to GM specs? To take off the switch and cover the 2 nuts have to be taken off the rear of the cover behind the dash. Best way is to take out the ash tray and it's much eaier to get to then. Don't use the Auto Zone stuff. The dealer is a couple bucks more but why waste on something that isn't to GM specs? While you're there with the plug off let's see if we're getting power to where it needs to be.
From the 3 o'clock position this is #1 wire then so on till #5 for reference.
#1- Ignition wire (pink w/ black stripe)
#2- Valve wire (lt. green)
#3- Tank Aux. (lt. blue)
#4- Gauge (tan)
#5- Tank Main (tan w/ white)
#6- Not used
With the ignition on you should get power with the #1 slot. If not check the pink w/black wire by following it to the fuse panel. Mine was connected with a male spade connector to a IGN slot. This way it's only powered when ignition is on (neing not running). Also you should have a light when testing for the #4 gauge as well (assuming it the #1 is hot).

If this doesn't solve it then take a test light to your fuel valve itself. It is located on the passenger side close to where the cab and bed meet. There are 3 different setups on the valve. They are 3 ports (fuel) 1 wire, 6 ports 1 wire (mine) and 6 ports 6? wires. You need to see which one this is. On the 3 & 6 ports with 1 wire, the green wire, attaches to a bolt coming from the valve itself. This is what powers the valve to flip from the one tank sending hose to another. When you have the selector valve on the left side (with ignition switch on and for safety engine not running and emergency brake on) the green wire will have power (where test light comes in). When you have it on the right side of the switch the wire will have no power. This is why I like to run on my right tank more often than my left. Now if you don't have any power to that switch under the bed, you need to backtrack (next section). If you do have power then you need to test the valve itself. With the ignition on engine not running and emergency brake on (safety first) take the green wire with connector to the "bolt" that is the connection on the valve itself. As long as you have power (with the interior switch flipped to the left side) you should hear the valve turn to the left tank. It sounds like a "click" almost. If you have power to the green wire but the valve is not changing tanks this is your problem. Replace the valve (I got mine for $70 from a AC Delco parts warehouse) and while you're there replace all the fuel lines as well. It's cheap insurance. Just make sure to label the hoses so you know which goes back on where. With 6 hoses on mine it was a job to make sure everything was on right.
On the firewall driver side look for a 4 wire harness with a bulk connector (looks like a connector that has a rubber boot) It will have 2 tan wires a green and a lt blue wire. This is where the tanks and selector valve wire come from the interior switch. If this is tight and no corrosion then we'll need to rethink this. Hopefully this works.
If you have a 6 wire then let me know and I'll try to find a spec for that then. I have't messed with that wire harness yet at the tank selector valve itself.

[Jim Molloy]

Hadn't checked the forum until today.

My truck is a '79 stepside with factory tanks.

I have power to the valve and it doesn't click ,so I'll get a new
valve.Only have one wire.

Seems like I saw 4 hoses but I'll check again.

Also I will check the back of the dash switch , maybe thats why
my gas gauge doesn't work.

Need to change the hoses as they are cracked badly.

To change the hoses the gas tank has to come down right ?

I can't see any other way to get to the tank end.

thanks for the help ...

[bpmcgee]

Jim,

You're right about the solenoid. If you have switched 12v coming to it from the switch and it still doesn't work, then it must be bad.

You are also correct that a malfunctioning switch could cause the fuel gauge to not register. More likely, though, would be a bad tank ground or a malfunctioning sender in the tank. To check this, jump the switch. Jump #4 to #3, and then #4 to #5. If the gauge starts working correctly, then it's a switch problem, otherwise the problem is something else.

Usually what fails is the tank ground or sender wire, or the sender itself.

Brian

[toomanybowties]

Ok heres my prob (hope somebody can help) I got a 1983 dually ,when the ing. switch is off fuel guage is going to about a quarter of a tank ing. swicth is on below empty on both tanks , I ve got only 4 wires dark green light green pink with black and black , the connector to the switch is rotted so I heat shrunk the connections , tried a new switch from a parts house getting a switch from the dealer , any Ideas????? p.s. I know there is gas in the tank

[79BIG10]

You might look at the wiring itself. Sounds like you don't have enough wires. Not sure if someone else has been in there messing with it before you or not.