Dual tank issues

[Rob Goblin]

This is my first square body, and I’ve never dealt with dual tanks before. When I bought the truck, the PO informed me that only the passenger side worked, and it was this way when he received the truck. He said he didn’t know why. I want to get both tanks working, but I’m not sure where to start. I’ve search the forum, and my search is not yielding many results. Perhaps my parameters are wrong. Please watch this video, and let me know if the fuel selector switch is good or bad or if you can even tell from the video. Thanks in advance.

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[Kim Burke]

The rocker switch is jacked up. It is supposed to flip and stay L or R. Right side is main tank. Does the gas gauge appear to switch if you hold the rocker in? If it does, the rocker may be your only problem.
Those switches are sock-sniffing cork soakers to get your fingers on. You’ll likely have to remove the ashtray or dash pad, either may break or cut you up. Good luck, my friend.

 

[Frankenchevy]

Ash tray isn’t too bad but may need to touch up paint on bottom screws if that matters to you. Anyway, just four sheet metal screws and it should gain you pretty good access. Either that, or it may be possible to contort to it without pulling the ash tray.

 

[ali_c20]

Changing the switch might help.

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If that's not working I would go trough checking the wiring and ground and if the valve is working.
Also check hoses and sending units.
Here is some usefull information:
http://67-72chevytrucks.com/vboard/showthread.php?t=754061

 

[Wumbo]

What does the fuel gauge do when you cycle the switch?

 

[ali_c20]

What does the fuel gauge do when you cycle the switch?

It should read the fuel level from the selected tank only if everything works and is wired correctly.

 

[Rob Goblin]

The rocker switch is jacked up. It is supposed to flip and stay L or R. Right side is main tank. Does the gas gauge appear to switch if you hold the rocker in? If it does, the rocker may be your only problem.
Those switches are sock-sniffing cork soakers to get your fingers on. You’ll likely have to remove the ashtray or dash pad, either may break or cut you up. Good luck, my friend.

If I recall correctly, nothing happens when I hold the switch. However, I’ll double check before work today to make sure.

 

[dvdswan]

Switch is bad as stated above. It should stay in the position that is set. Only two positions. The switch you have seems to be a rear window switch. Three positions.

Be sure your wiring is correct as well.

 

[Rob Goblin]

I did a check and nothing happened when I held the switch in either direction. There was no fluctuation to the fuel gauge. I guess my next step will be ordering the switch. Could someone tell me how to tell if the wiring is correct? I know at some point the wiring under the dash was cut to install an aftermarket radio. The radio isn’t there anymore, but I can see the wires where it should be.

 

[Rob Goblin]

Could someone tell me how to tell if the wiring is correct?

I can’t read wiring diagrams to save my life. I do better with hands on visual than color charts.

 

[dvdswan]

Fuel switch is circled. I don't remember if this is the back or front of the connector to the switch. Each lead is labeled and color wire coincides. The top of the connector is the top on the diagram.

Lead colors:
1. Ign. feed - pink/black
2. Solenoid - (switching valve under the truck) - light green
3. Aux tank - (fuel level from tank) - light blue
4. Gage - (from cluster) - tan
5. Main tank - (fuel level from tank) - tan/white

It really is very simple. The wires are probably in the correct positions and you are just using the wrong switch.

BTW, this is from the 77 manual but I don't think GM changed colors. This is just what I had on immediate hand and couldn't download the 84 from the site at work. https://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

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[lothar863]

The switch is bad as stated but there are a few different part numbers. It took me a couple tries to get the right one for my truck and even then i got a couple that were defective. But all of them clicked and stayed in place.

If the gauge doesnt move that point to either a problem with the tank switching valve or the sending unit in the tank.

The tank switching valve is under the truck on the passenger side behing a heat shield on my truck.

I found a number of issues created by a previous owner trying to get the drivers side tank to work where they just made it worse.

Pm me and i can share my expirences if you like.

I think i have the part numbers i used in my under construction thread if that is all you are looking for.

 

[Dubo93065]

I changed the switch, selector valve, and Harness for the valve on my 82 K1500. I still had problems switching tanks. Here is what I found that took a lot of time and money on parts I did not need. There is a connection on the firewall near the accel. cable for the valve (two wires) that needed to be cleaned and the male connectors pinched to fix connection. The tanks work great every since.

 

[Truckbuild]

Here's my experience with the dual tank setup on my k10. Maybe something will help you. On my 84, I had issues where the tank selector valve would only go about half way on either tank. So when I needed to step on the gas to go up a hill, the engine couldn't get enough gas, & would stall as soon as the carb bowls emptied. So, since I had both tanks full, I got to siphon both of them out, & drop them. There was rodent chewed wiring on the tops of both sending units on both tanks, and every one of the many fuel lines were dry rotted & leaking. Needless to say, neither of the fuel gauges worked. I fixed the wires & hoses to get my gauges to work, the selector valve fixed my fuel starvation issue. If you get your possible wiring issues figured out, you should be able to hear that valve switching as you work the switch with key on, engine off. Very likely your truck needs attention at the tops of both tanks. Also, my 84's selector switch springs back to center from eiher side, I just replaced said switch about 6 months ago, so it's action is correct. That is an AC Delco switch.

 

[Rob Goblin]

Well guys, quite a bit has happened since I last logged on. Needless to say, I haven’t messed with the truck in a while. Actually, I drove it for the first time in months yesterday. I replaced the switch. It was broken as it fell apart when it was taken out of the dash. The new one works as it should, but I still only have a passenger tank. My dad called me a few weeks ago, and said he found me a great parts truck, so I thought I’d rob parts from it. However, it’s an 86 and runs great. I’ve only driven it a few times around the neighborhood though. I did notice the selector switch is different and in a different location. I also noticed the engine is like my dad’s 87 minus the throttle body. Anyway, I’ll check the firewall today as Dubo stated and see if there are any changes.

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